well most slavers and raiders don't have kids right? remember that raider quest where you have to kill that ex member of the raiders who just wanted to retire... that gives me the impression that Raiders and what not aren't technically allowed to have a family and a life or kids (since it constitutes as "retireing"...
anyhow sometimes I think people think a little too outside of the box for fallout online... "So if you kill any child, raiders/slavers respect you more ? (And what if it's their own child, by the way ?)"
Le'ts get technical, If I kill someone's child he will want revenge. Just because the Raiders respect me more bcuz I am such a cold hearted MF that I can kill a kid and not care that I kill kids, doesn't mean I am the guy thats gunna go around killing their kids.... It simply means my character has no heart... therefore Raiders and such (people with no heart) will respect me more.
The Childkiller perk is an evil perk which means evil characters should get along with me more...
Remember this isn't reality its fallout and fallout is just a game that isnt realistic