Considering idea about children while they may be innocent but their parents or caregivers may be assholes and murdering those assholes will pretty much kill those children too.

In same way murdering someone you don't like, may cause lots of pain to someone who you actually like and don't want to hurt.
As it woud be not very nice to kill your friend's dear wife who is a feminist just because you hate feminists.

But I guess if extermination is performed according to my standards those kinds of things should not happen because friendship takes priority over morallity.