How open can an open adoption get?

We adopted our DD(now 5.5 yrs old,she was 18 months when she came to us) through foster care, so it took time to develop a good relationship with her bio family. This past weekend her first Mom and Dad took her to the mall and the playground with her younger brother, who they are raising. This is the first time that we have allowed them to leave our house with her. We go visit them(about 75 miles away) about every 3-4 months. We know grandparents,Aunts, uncles and all sorts of cousins. I forsee a future where she will be able to go places with them and possibly stay at their house. Her case is not the usual foster care story in that the parents do not and have never done drugs, nor have they ever abused her.