I know its possible that kids die there are animations for it.
I was bored at this kids party, and after getting the bb gun and killing my dad with it I escaped that room where you get your BB gun, I unlocked the door with unlock cheat and went to the door the overseer went after the party. I unlocked that door with the unlock cheat too and walked through, because they didn't create the vault as a whole while being a kid there is a huge amount of empty space, you'll see the overseer stand on a small patch of floor, if you walk into the emptiness you will fall down and fall into the corridor when your dad escaped and the radroaches are everywhere.
There will be no guards that will attack you the overseer and amata won't be anywhere in other words there will be at that point be no NPC's whatsoever only roaches, I killed them all and 2 the overseers office, you can't lockpick but the overseers key should be in the dressing cabinet in his room, you can open the door to the office, there should be a password in one of those lockers so you can open the overseers tunnel.
Then you will go to where the secret passage is and discover that a child cannot handle the switch. so I used the collision cheat and went through the wall anyway, after that I kept the collision cheat on and went through the vault door (you cannot operate the vault door system as a child).
There after I just walked to the door after toggling the collision cheat of and opened it and chose the option "Finished - leave Vault 101" so I entered the wastelands as a full grown 10 year old, went to megaton said there was a new sheriff in town and got owned and killed, automatically reloading the last save as he would if you were an adult.
So the ones not believing my story try to reenact it either way you will see that kids CAN die
yours faithfully,
CrazyDawg