I have a son and I was just wondering what rights my adoptive parents have over him?

The same rights any other parent would have. Adoptive parents are legal parents.

What EXACTLY are you asking, here? What's the situation?

This is controlled by state law, so it really depends on where you live. But generally grandparents have few rights with respect to their grandchildren (I assume you mean visitation rights), especially if the parents are alive and competent. However, the court may grant visitation rights if the grandparents can show that the grandchild would be harmed otherwise (i.e, by demonstrating a history of close relationship between grandparent and grandchild, and that the chid would suffer emotionally without this continued relationship). For reference, here is a discussion about grandparent's visitation rights in Illinois:
Grandparent visitation rights Illinois involving grandparents visitation Illinois: IL grandchild visitation. (http://www.goldberglawoffice.com/grandparentVisitation.php?gclid=CM7Ns77Ao6YCFUyD5Q odMT_lnQ)

The question may not be about visitation rights, though.

It may be about whether the grandparents have the right to be next of kin on a piece of school paperwork, or whatever.

That's why I wanted to know what the situation was before jumping to conclusions about what the OP is really asking.