It is normal to feel some jealousy when your ex finds someone new. This is a very common feeling when you do not have a new relationship. The key is knowing if it is just a little touch of jealousy or if it is real feelings. The fact is he has moved on......even if he still cares for you he has accepted that it is over, so be careful where you tread. It would not be fair to him or you if you swoop in and take him back then decide you do not want to be with him after all.
Having a child together is a big bond, one of the biggest you will ever have with another person. And it is normal to want to make that bond into a family. The issue is can it be? I would suggest you sit down and make a list of all things you loved about him and your relationship. Then make a list of all the things that were wrong or you did not like. Once you are done give some thought about what you want in a relationship and a mate. Does these things consider with the things on your lists or are the things on your list causing conflict with what you want?
The reason why I ask you to write this down is because it is easier to look it over and think about each thing while writing it down and once you look it over. It will help clear the feelings on the matter and give you a chance to see everything in black and white and help you decide what you really want.
If after doing this you decide you really want to be with him then give him a call. Let him know how you feel and ask him if you can talk with him about it. The key is make up your mind before you call him. It is not fair to him to be told you care and then change your mind. Think long and hard about what broke up your relationship in the first place. Is this still a issue? If so then that is something that will have to be worked on before you can make this work.
In the end it takes time to get over someone fully, if this is just some jealousy issues then it is better to allow him to go and give yourself time to move on.