Why do I think my kids are so cute, but I think everyone else's kids are pugly?

Seriously, I can't look at my own kids and think that they are the cutest kids I have every dealt with. On the other hand, whenever I look at someone else's kids, I think that they are pugly or annoying and I don't really want to interact with them. Is this some kind of built in mechanism in our brains that makes us "over-focused" on our own children? Maybe I'm just a jerk. A classic example would be when my daughter plays with the boy from down the street. Seems like a nice kid, but I find myself basically ignoring him for reasons I can't completely understand. Not that I'm neglecting him (my wife is present when they are playing), but I just have complete indifference toward him and other kids.