Make him fight for visitation, especially if he's giving money. Document everything he gives her.

well maybe you could try and set up a lunch or meeting or something with the girls parents? and start from there
get together and try and talk to them and let them know that you guys are willing and wanting to help in anyway possible

as a father your son has the RIGHT to be in his childs life and unless she has a court order saying he cant then she has no right to keep him from seing that baby

definitely try talking to the girls parents, also be prepared to have to get a lawyer incase you have to fight for visitation or even establish paternity because if she doesnt put him on the birth certificate youll have to request a DNA test to get on it and get the visitation rights.

It sounds like your son is trying to do the right thing and by supporting his decision to be a part of this babys life and wanting to be a grandmother for it your on the right track

So she just found out she's pregnant, right? Like within a few days? Because depending upon the day of conception, the due date is around 8 months away, right? Maybe she is just in shock or needs a little time.

who knows

girls are wierd

Why is he giving her money already? Is he sure she has decided to keep the pregnancy?

maybe for medical bills, to start buying stuff for the baby,etc

Gotcha.

Do you know for certain that the child is his? Maybe she has gotten into another relationship?

If for certain the child is his then petition for custody?

I don't think a petition for custody would be the right way to start this, as you may be able to do it on friendly terms.
I think the idea of a lunch with you and your son, the girl and her parents to begin with would be a smart idea, try to keep it friendly, maybe not even bring up the baby just make friends with them so that it's easier to get that visitation later.. once the babys born they'll probably be dying to let your son take him/her for a while so they can get some sleep