*All* of the older children gravitate towards the babies in my daycare groups. It's not at all unusual. The only ones who ignore the babies are the children who are babied too much at home and are demanding about wanting all of the attention themselves.
But anytime there is a baby in the group, the children will even push to be the only one playing with the baby. They all want to mother them....even the boys. They all want to do things for them....even so much as to get diapers for them to be changed and such.
Often, I have to send them off to play with their older counterparts. And if the babies cry or awaken from a nap...they are right back in the baby area wanting to help and entertain them. I think it's because they want to feel older and try to mimic the adult who is providing the care. I think it's good for them to learn to be caring and loving towards the younger children.
He'll become more social with the older children when he's a little older. Learning that he can go outside to play with his older friends...and do things the babies can't do, will eventually change his interests. He already enjoys his friends in his play group.
This sounds so typical of the children I've dealt with over the past 22 years in child care. Not at all unusual. In fact, some parents have problems with older siblings trying to do too much for their new babies. Lines have to be drawn as to what they are and are not allowed to do.