What This Thing That My Son Has Towards Babies?

How do YOU respond to babies?? Are you all gaga over them? Focus all your attention to the baby? Have you been wanting another baby? He might be picking up and getting jealous over loosing your attention. If you have a friend with a baby I would sit on the couch with my son and the baby....say things like he's cute but he's not you. With your CLOSE supervision maybe have him hold baby. See if you can work out a regular visiting schedule.
I would defiantly keep a close eye on the aggressive behavior though. If it starts to make warning bells go off or scares you you should seek the advice of a professional. Good Luck.

This sounds like pretty normal behavior. He doesn't want anyone--inlcuding babies--to take his stuff and he acts out when he feels threatened. 5 year olds aren't exactly reasonable when it comes to assessing a real threat. Obviously a baby is not going to take his toys-but you son isn't getting that. I think you need to step in and teach your son that it is not okay to hoard toys or lash out at another child--no matter their age. Instead of watching him like a hawk when a baby is near--teach him the appropriate behavior. He is old enough to know that hitting or pinching and mean faces are not acceptable. If he does this he needs to be disciplined by removing his toys and given a time out or leaving the situation entirely. Phase or not--his behavior is poor and needs to be addressed.

My younger daughter has never liked babies (she's almost 5 now). I think it's because she is super cute herself, and she doesn't like the competition for the "cutest person in the room" award! LOL

It started to get better when her little cousin (now 2) began walking and followed her everywhere. We kept telling my daughter, "Look! Baby Lilly loves you SO much and wants to be just like you! She thinks you are so cool because you're the big kid!" This helped her see herself as the wise older one, I think. Still though, she is not a super huge fan of tiny babies that everyone fawns all over. As Mariah Carey once said, "The divas have been divas all their lives!"

Sounds like normal territorial behavior. Is he around smaller children often? I went through something like this with my middle son when he was 3. He became terrified of his baby cousin. She was a baby and he would scream and growl whenever she was near him. He wanted nothing to do with her and would cry when she got too close for his comfort. What we did was allow him his space so he didn't feel like she was taking his place but we also would allow him to help out with her and explained that she was a baby and that he was our Big Boy....after constantly telling him that he was our Big Boy he felt more like a big kid and less like a baby....meaning he did not feel like she was competition for him anymore..