I discovered that on DDB stablocks for wormlings and young dragons include the writeup for lair actions and regional effects, despite the fact that the introductory section of the Monster Manual specifies that lair actions and regional effects are only for legendary creatures: adult and ancient dragons are legendary, young and wormlings are not.   This is backed up by a Jeremy Crawford tweet.  Furthermore, the section in the dragon entries on regional effects specifies that they only apply to legendary dragons.  Why are these include for young dragons and wyrmlings?

This isn't a bug. It is how it is in the physical book.

Your question needs to be put to WotC , who will probably ignore you because I've already pointed this out to them years ago, as have others, and they don't give a shit.

Quote from Cyb3rM1nd >>

This isn't a bug. It is how it is in the physical book.

Your question needs to be put to WotC , who will probably ignore you because I've already pointed this out to them years ago, as have others, and they don't give a shit.

 Interesting....I no longer have easy access to the physical book; I guess I made an assumption how it was laid out there.  Thanks for cluing me in!

Apparently, I just needed to be patient.  From the new Fizban’s support thread:

All Wyrmlings and Young Dragons. This book provides guidance and clarification that Lair Actions & Regional Effects only apply to Adult & Ancient Dragons. As such, all Wyrmlings and Young Dragons have had their Regional Effects & Lair Actions removed.