I got out of the vault as a 10 year old girl named Betty using the tcl command.
She has all the animations of an adult, but has a little girl's body.
She can accept and do all the quests.
She can wear any armor in the game, but the armors do give her small breasts.
She can use any weapon in the game.
She can use any drug in the game.
She can wear sexy nightwear, but the outfit gives her large breasts and reveals her brown undershirt underneath.
She has clipping problems with hats and helmets.
She can be damaged and killed.
She is definitely classified as a child. For example, she cannot interact with certain items, such as the bomb in the center of Megaton. When she tries to do so she gets the msg: "children cannot interact with this object.' So, with respect to this particular quest her 'child' race is a restriction.
The fact that she is killable tells me that there is another variable not tied to her 'child race' which could be toggled on/off to make children killable. I suspect that the children NPCs have simply been given the same 'essential' tag as NPCs involved in the main quest. So once we know the code to toggle that off, killable children will be in the game.