B.H.
Hi B.,
I am not sure what the law is in the USA, but in Canada, the role of the god parents is only figurative unless there is something in the will. We have had both our children baptized with god parents (my sister and my husbands' brother) and all that really means is that they have a figurative responsibility but in the eyes of the church of course is different.
Being a "god parent" is about them teaching the lessons of god. Whatever ceremony you do, is for you and your religion. I think if you really want it to be offical, like if something happens to you they will be there for your son, you need to get it in a will. AND everyone you know must be aware of your wishes.
Congratulations with your lovely family.