Child

Children are the young inhabitants of the wastes.

Background
Children may be killed in Fallout and Fallout 2, which earns the player the Childkiller reputation. In later titles, the Lone Wanderer is the only child with possible on-screen death, during a virtual reality simulation at Tranquility Lane in Fallout 3.

Children in Fallout 3, Fallout: New Vegas and Fallout 4 are marked as essential, however, they are also coded so that they cannot be hurt by any kind of attack. They will react to the player character or another NPC assaulting them, always fleeing instead of retaliating against their assailant. In Fallout 76, children do not respond to combat in any way and cannot be damaged.

Fallout 3
Children cannot be targeted in V.A.T.S. However, if they are accidentally injured, they can sustain crippled limbs. Since children cannot be harmed, they will generally not fight the player character, even if they are armed. Instead, if attacked, they will flee. The Mister Sandman perk cannot be used on children.

Fallout: New Vegas
Attacking children results in infamy with the faction they are associated with, even though they cannot be hurt. The Mister Sandman perk cannot be used on children.

Fallout 4
Children cannot be killed or targeted in V.A.T.S. The Mister Sandman perk cannot be used on children.

Fallout 76
Children are flagged as "ghosts" and are not part of the combat system.