Well that's what I'm thinking, what makes the Goblin children so evil that its ok to kill them but not other races children?

Being raised in a society that tells them its ok to throw rocks at a bear?

Surely the solution isn't to kill them for that, but to rescue them from such a society, maybe by adopting them into a better one.

Or making efforts to increase the social inclusion and welfare of Goblins as a whole.

But hey if you're going to just sit there and go 'Its just a game, its evil goblin kids, so what if you kill them?', then let me also be able to kill the tiefling kids too?

Would it be ok to Kill Shrek's kids because they're ogres or some such? And in fact Shrek should demonstrate the whole reason why the idea of 'good races vs bad races' is inherently flawed.