It's quite possible to lure the child slaver out to her death by bringing Bumble outside from Little Lamplight. This does not seem to make other slavers hostile. The Lone Wanderer suffers no Karma loss and since the 'necklace' is never placed on Bumble, Bumble will say "I don't like outside. I'm going home", and return to the caverns.
Killing the child slaver before luring Bumble or any other young child from Little Lamplight will turn all slavers hostile. However, drawing nearby super mutants to her, and letting them kill her will not.
Killing the child slaver after luring Bumble or any other young child from Little Lamplight will turn all slavers hostile. Bumble will run back into Little Lamplight and stay there with the slave collar on. Somehow, her collar never explodes despite not going to Paradise Falls.
200 Karma will be lost as soon as the collar is placed on the child.