Is it a natural Law of attraction!

THEY DON'T! Sometimes even boys love their fathers and girls love their mothers. And sometimes they're equally loved by both. It just depends on the members of the family. Maybe in your neighbor's case the father is the type who thinks boys should be independent and rely on themselves, so when the boys are in trouble or for example want money, they go to their mother. So naturally they will be more comfortable around her and will want to run to her all the time. And maybe he thinks girls shouldn't be as tough and rough as boys, so he likes to play with them more often or he's a lot more easy going with them. So it's different from one family to the other..