So, I'm rather new to DMing and my party likes to split. In the last session, they were only 3 and even then, 15 minutes in, they were already each in a separate section of a cave network. They did end up regrouping eventually, but it took time. During that time, I wasn't sure how to handle them. I kept freezing/unfreezing everyone and cycled among them managing each for a bit before changing to another.
With only 3, this method worked, but they're supposed to be 6. I don't think it will work if five people have to wait for every person all the time. Even in combat, it's hard at times. I don't want to force them to stay together though; at least to a certain extent. I won't allow them to split and go for entirely different quests because that would be impossible for me to manage, but splitting while exploring such a cave-network seems logical.

How would you handle this? Any tricks for handling splitting? Thanks in advance.

Sounds like you handled it fine, and I would be very up front with my players "if you wander off on your own you will get 1/6 of the time focused on you, long wait for it to be your turn again, and you might bump into more enemies than you can survive". If they are happy to play like that not stick together for mutual protect and have the focus on one group the whole time that's fine so long as you are happy, if your not then just tell them don't split up so much I can't divide the  focus fairly and keep the session going at a pace I am happy with, I doubt they would be unhappy about it they probably haven't even thought about it.

My party liked to split up a lot in the beginning of the campaign. I feel you.

Subtler things you can do:

1) Create puzzles/traps/doors that require the whole party. (Doors that need the combined STR scores of the group to open, traps that need multiple people standing in different areas of a large room to disable, puzzles that require martial and spellcasting talents from several people to solve...etc.)

2) Make it dangerous to split up. Send them monsters that are deadly for 2 people but manageable with 6. Trap the splinter group (cave-in, quicksand, reversed gravity shaft) and keep them there for hours until the party has to rescue them. 

3) Have the wrong group meet an important NPC. Maybe there's a spy who has information for the rogue, and he'll fight his way through anyone until he finds them. Halfway through the fight, he drops the rogue's name. Oh no! This whole thing was a misunderstanding! We're friends with the rogue! Stuff like that.

Overt things you can do:

1) Have friendly NPCs tell the party they're foolish for splitting up. If an allied NPC is traveling with the group, you have a mouthpiece. 

2) Have a chat with your players. This is what I eventually had to do. I explained to them that sessions were only so long and it was difficult on me to keep pausing the action for one group to run a completely separate scenario for another. I reminded them that this is a cooperative game with encounters designed for the entire group, and that it's neither fun or fair to be a spectator when you are there to play. I told them I was fine with occasional splitting if it made sense in the story, and that they could do whatever they wanted in downtime, but I requested that they try to stay together so that their characters could form bonds and learn how to partner up. They took it really well and I haven't had problems since.

One of the first rules of DMing is "Don't split the party" -- which means that as a DM, you shouldn't plan to split them up. But if the players are doing the splitting up... not sure how much you can do to force them to all go together from one place to another.

Option 1, and probably my go-to recommendation, is to talk with the group of players OOC, maybe at the start of the next session. Remind them all that you are new to DMing, and that as a new DM, you are having a really hard time handling having multiple things going on all over the map, and managing how to cut away from one to another and still keep the session flowing. Ask them if they, as a courtesy, would please try to all stick together unless there is some compelling in-character reason why they would split up (such as sending a rogue ahead to scout). Any group of players that has any sense of manners and cooperation should agree not to split up on you anymore.

Option 2, which is more the "old school" way to do it, is to just put stuff onto the map that is going to be "deadly" or nearly so even for the whole party. If they each encounter something powerful enough to face the whole party as individuals in different parts of the dungeon, they are going to be in some serious trouble. Maybe this teaches them a lesson, though it also has a high chance of killing multiple PCs. Don't deploy this option unless you are prepared for the fallout (both in terms of dead PCs and them having to make up new characters, and the inevitable anger the players will have at their PCs dying). Now, their deaths would be their own fault, but in my experience, the only thing that makes players angrier than dying through no fault of their own due to a killer dungeon design or something, is dying when it is absolutely and entirely their own stupid fault.

Option 3, which is a much gentler version of option 2 but consequently has less chance of making an impactful and lasting impression (and thus may not solve the problem long-term) is to put some kind of a puzzle into the next part of the dungeon that takes all 6 of them to solve (trouble, if not everyone shows up, so make it "moddable" to whatever the party size is). For example, a mechanical bridge to cross a bottomless chasm, and the only way to extend it is if everyone simultaneously pulls on 6 different levers all at once. A solo PC can't do that, and they would have to gather up. This could hint to them that they need to all be together and maybe they stick, but the problem is after they get past the challenge, they can split up again potentially without consequence.

I'd say if you are going to deploy option 2, maybe try option 3 first to at least hint that being alone is a bad idea.

Personally, I would go with 1 first.... but the reality is that for most of my dungeons, option 2 is already baked in and I have told my players from day 1, I will NOT do anything to save them from their own bad decisions. I took it easy on them a little in terms of dungeon design (simple, not super tough challenges) until level 4. I told them this. At level 4, I said, all gloves are off. If they wake up the entire dungeon and bring it down on their heads, or if they split up and all trigger separate encounters meant to be barely survivable by the party, they will probably die. Not going to save 'em. So just naturally, my dungeons are all made to be Option 2. Fortunately their instinct is to stick together, so we have not had this issue. But I feel like if they started pulling this stuff, the next dungeon would just naturally solve the problem for me (and they'd be rolling up new PCs... oh well, they were warned). 

The thing about having done this kind of design is that they have seen first hand what is there and they can all tell, without really having to talk about it, that if one of them had gone alone in this room or that building, that PC would not have come back out. So they just naturally stay together.

Not all traps kill.. and actually, if I were a trap maker and had to live next to it.. it would "Trap"

DM "So you are searching the section of the wall in the left-hand tunnel,  how are you doing that?"
PC#3 "Blah..blah.. blahh."
DM [hands prepared paper; "The surface of a pit trap breaks and you start to fall; acrobatics check" ]  "Roll a 20"
------[ hands prepared paper; "The Roll fails, but you land in what is 2 feet of mostly dry bat guano (poop), so take no damage. You get three tries to climb out starting next round; this starts at dc15.  with +2 each time PC# tries.. as you just have just found where the wet stuff is coming from.. the walls. ]
DM "Okay PC1;  "So you are searching the section of the wall in the middle cavern,  how are you doing that?"
 . . . time passes. . . 
PC1 asks PC 2 "WHere is PC3?"
(Player 3 looks at the others, considers their PC covered in slimy bat poop, and thinks about the layered pile of sticks and twigs above having fallen in blocking sound from getting out.  Smiles saying nothing.. knowing from a note that they get a bonus check at original dc if they give no hints.) and rolls another 1d20
DM "don't look at me do you remember where they were"

That's more or less what I've done already. There were multiple "small" encounters that they faced, as well as a trap, that should have made it obvious that going alone is dangerous. They still went on alone and one of them died (6 1st level characters fighting one mimic is possible. Solo? Not so much). I think they've learned that lesson, but I expect them to keep splitting but be more careful... it's the kind of people most of them are.

I know talking to them and asking them to stay together is the easiest solution, but I wanted to see if anyone had a better way of handling it when they do split up. I'm not sure what kind of answer I was hoping to get tbh, but it can't hurt to ask.
Thanks for the feedback. I'll see if they keep splitting like this the next session too. I expect at least two of them to understand, at this point, that splitting is actually dangerous and try to stick together as a result. Maybe they'll surprise me though, can't say for sure.

Talk to them. Explain to them that D&D is a "team sport" not a solo affair. If they refuse to stay together, then calmly and very politely ask who would like to start DMing.

Honestly? Talking to them is the best option. Training them not to split up will take time and may not work, and there really isn't a way to run a split-party session without handling one scene at a time and pausing the rest. You're only one person, after all. 

Best of luck!

I find the best way to deal with parties that split up is to let it play out. If they run into traps, fights that they need help with, anything where one character can't deal with the situation (and that is often most of them) then the players will often get the message that it isn't the best tactic and will self limit except when it really is a context when the character would try to go off by themselves.

However, this does mean that the DM and the players need to be aware that their characters can die, that they may encounter things that will be deadly if they are by themselves. Character should generally stick together because there is safety in numbers and each brings different capabilities to solving any problems encountered.

This approach though does mean that the DM has to make clear to the players that the world is a dangerous place and that if a character encounters something that they can't handle on their own, the DM won't be stepping in to rescue them. Sometimes just making the situation clear to the players will encourage them to stay together. Sometimes a close call or two is sufficient and occasionally a character will have to die before the players realize that there are risks to solo adventuring.

I have no issue with my party splitting up generally, I don’t run dungeons at all so the whole world is a big open playground. My players have no issue sitting and just watching the other group as they play through their bit of the campaign. Generally it is the non combat stuff, so investigating the town, going and talking to people, shopping trips (my players love role paying shopping) but in the past I have purposely split the party in 2 where 2 things had to be completed at the same time and then run seperete sessions for each smaller group. 

Oddly as a player I have a tendency to have at worst semi-professional heroes.. would; as such prefer to have a reserve sit back and "watch" the others.
which splits it even more.. Prefer in-sight but (SOP) message cantrip would be useful.
Once had our party split into three parts for two days: Reserve base; in-sight of the archer Ranger in a tree, who in turn watched the Thieve's hide, as he in turn cased the dungeon site.
(Watching wandering monster rolls; and their traffic.. We hit the dungeon at the back door.. and ran through the published dungeon back words.)
* * * * * *

While you as the DM can talk to the players.. it is possible for PCs to meet ex-professional hero "contacts" who can advise on safer party techniques. 
Say some NPC misses drinking with his old [deceased] dwarf partner, and is willing to buy drinks for the party's dwarf, and tell stories.  (and DM sets Moral-of-the-story)

Have a Guild thief Yakuza rogue.. from a big city, on another world; who won't "Finger" in the city-square since his home guild forbids "picking" in public without a team; a "bluff" [performer to draw attention], a "switch" to pick the bait from the finger, and a "Finger" to pick the bait from the "Trap" [owner of the bait]
The whole thing is so each roll in the servers  pickpocketing system is with assistance.
He though a PC, complains about the Lack of Local Professionalism; much like an EX-hero npc might.

My party split tonight, as it happens. It was an investigative one-shot (though it's starting to look like it'll end up as three sessions 🙄), and it made sense for them to split. Thankfully it all tied back together as their individual threads converged and it worked well. 

But then they tried to split again for a bad reason. I leveled with them and said if they really wanted to, they could, but as DM I'd appreciate if they didn't. I pointed out that the location they were sending half the party to really had nothing for them, and was honest that I'd struggle to find something for them to do, and they'd be effectively just cutting those PCs out of the session and it wasn't really fair. They took it just fine and stuck together. 

Otherwise I'd echo the advice if others. If the more subtle approaches don't work, start killing (or at least knocking unconscious) PCs.  Adventuring is a dangerous business and your encounters should be balanced to the full party. A trivial encounter for 4 PCs can be deadly for 1. 

I don't understand this thought of "Don't Split the Party Up" attitude. Sometimes it is strategically advantageous (for flanking maneuvers, three characters enter the domain of the big bad from the east and three enter from the west, but, the party has to split up for an hour or two to accomplish this).

As a DM, I've designed traps whose sole purpose was to split the party up.

Yes, it does create some problems for you as DM, but, the payoffs can be incredible. When I've done in person DM'ing, I sometimes gone into another room with the PC or PCs to resolve their situation. Players who normally stayed in the background and didn't say much would be forced to make decisions. This would sometimes give them the confidence to start making decisions in the larger group.

And, I would think that intelligent big bads would want to split the party up. Get the barbarian and paladin away from the rest of the party, and hit them from a distance with spells, arrows and other forms of distant attacks. Get the spellcasters away from the tanks and force them into close combat. 

It basically gets the players out of their comfort zone and can be good for the overall game.

Quote from Siyaj_Kak>>

 

Yes, it does create some problems for you as DM, but, the payoffs can be incredible. When I've done in person DM'ing, I sometimes gone into another room with the PC or PCs to resolve their situation. 

You do you, but being left in a room alone is not as much fun as you think it is.

 In an encounter yes, in a dungeon not so much. There is only one of you and for every split you form, you are alienating the other parts of the party. If you can do it and your players are having a good time, way to go.