Depending on the choices my players make, they could end up in an adventure where they get transformed to tiny sized in order to infiltrary a base filled with tiny sized creatures.  There are a number of magic items (including at least one weapon) all sized for tiny sized creatures.  I'm trying to sort out whether or not said magic items would be useable by my players after they leave the base and return to their normal size.  What do you all think?

Well, that’s a good question. Normally magic items “resize to fit.” A Gnome and a Bugbear could use the same boots of elvenkind without any issue.

I think it might depend on the specific magic item and what it says as to why/how it is specifically for Tiny creatures.

Yeah, I'm pondering making the choice on a case by case basis.  I'm a little hesitant to give more specifics, because my players all have accounts here and three of them also DM their own games, or at least have in the past.  I don't think any of them are very active in the forums, and none of them would intentionally cheat and read up on things here, but it's conceivable they could stumble across it and not realize they are reading spoilers until it is too late. 

There's no right or wrong answer here. After all, the PCs' clothes grow and shrink with them, so magic items on their person certainly could too. (And the idea of, say, a magic needle, used as a sword by mice, growing to human size is pretty funny.)

But if you want the items to be temporary, that works too. In fact, it might even be more logical, since the reverse-shrinking isn't a "grow" effect but a "remove shrinking" effect, which wouldn't touch things that weren't shrunk. It's really up to you!

It simply depends on your personal preference and how the shrinking effect works. I see several options:

A) A temporary potion, shrinking the players but none of their equipment until the potion wears off.

B) A temporary shrinking spell, shrinking the players and their equipment, but only shrunken items return to their full size when the spell wears off (Or when dispelled).

C) A permanent shrinking spell, with a corresponding growth spell. The shrink spell shrinks the players and their equipment, the growth spell grows the players and their equipment. Basically, if you shrink and drop an item, then pick up a different item, only the item you're holding would be affected by the growth spell.

But like NaivaraArnuanna said, there's no right or wrong answer. It's up to you.

That all sounds very Alice In Wonderland, with a Shrink Me potion and a Grow Me potion.  I don't see any reason why magic items shouldn't change size to suit.  There aren't quite rules for tiny creatures in combat yet, but they are on the horizon, so a poke into the Unearthed Arcana forum might be helpful.

Quote from Geann >>

That all sounds very Alice In Wonderland, with a Shrink Me potion and a Grow Me potion.  I don't see any reason why magic items shouldn't change size to suit.  There aren't quite rules for tiny creatures in combat yet, but they are on the horizon, so a poke into the Unearthed Arcana forum might be helpful.

 The tiny creatures in combat thing is sorted; the adventure I'm using has scaled the inhabitants of the base into "medium" sized creatures so the players don't have to change anything about their stats or attacks.  

Thanks for the input and suggestion.
To clarify, since it sounds like there is some confusion.  I'm not concerned about magic items etc. that the PCs already own: those will resize with them both directions.  My question is about the magic items that they may find in the base itself.  Obviously, while they are tiny, they can use them.  I'm just trying to decide whether those things that are tiny by nature, not by magic, would resize with the PCs.  For at least one of the items, I can see a logical explanation of why it would.  For the others I'm less sure.  

Quote from ArwensDaughter >>

For at least one of the items, I can see a logical explanation of why it would.  For the others I'm less sure.  

 Honestly, your players are unlikely to care too much about the specific mechanics of the situation. Handwaving it as “magic” won’t hurt their enjoyment.

What they will care about, though, is if they can only keep some of the items, especially if they’ve already shared them out amongst themselves. So whether it makes sense or not, I’d suggest they either all grow or all stay small, or you’ll have some very disappointed players on your hands. They could even think you’re playing favorites.

There would be nothing wrong with having the items they find be only useable by tiny sized folk. The Dungeonland module did this. You could find really nice magic items but when you went back to your normal size, they stayed tiny. 

You can answer your own question by deciding what the point of adding these items to the storyline is. Should they, could they be a reward? Would their usefulness supersede the usefulness of the items the characters already have? Do the items have a specific purpose like solving a puzzle or the only thing that can kill BBEG? Are they just cool extras while in the tiny realm only?