My grandsons father had full custody and he let (grandparents) have custody with a written agreement also pays child support. Do we need to do anything else in the courts to make this legal?

I don't know where you are but I would take it to Court and let support and custody be Court ordered on YOUR terms - you already have an agreement.

I live in IL and we had written agreement written and both of us signed it. Another question is does it require getting a lawyer to get legal guardianship or can I file the necessary forms?

I would do none of this without an Attorney - these family court problems can cause terrible problems in the future if not done properly. Take your written agreement to family court and ask the Clerk how to turn it into an Order.

The Courts take the position that children are not puppies - you cannot just change "ownership" without the consent of the Court.

I understand why you are doing this and I am NOT criticizing you - I am just saying that there could be pitfalls down the road.

First when posting a follow-up question or info, please use the Answer options at the bottom of the page rather than the Comments.

Such an agreement is generally NOT binding unless ratified by a court. So you should go to court to get them to sign off on it.

Sorry you can not change or give custody by signing a agreement unless that agreement is signed off by the judge.

Next just because he has "full custody" does not mean he can sign custody to someone else, without the other bio parent agreement. Full custody is not complete custody, since the other bio parent has rights ( from visitation and so on)

Next only the court can order child support.

So the paper work they did has no legal bearing what so ever.