I remember last year hanging out with my friend's son. She brought him along last minute which had me worried. I ignored him for most of the outing, though he seemed to want my attention and held my hand when we were walking. By the end I ended up liking him more than his mom, ha. My friend said a couple of bitchy things to me that day, and this boy was all sweetness.
The trick is to play with them. Ask them questions. Kids can get really animated and like the attention. I am actually doing a disservice to myself by not hanging out with children more often. With babies, I guess it comes down to telling the parents how adorable the child is and ask to hold them. They seem to like that. Sometimes I feel like such a robot, having to learn the proper ways to behave -__-