Is it normal for a foster brother of 16 to spank a 4 yr old foster

My 4 yr old grandson is in a foster home and soon to be adopted im not for sure if it is finalized as of yet it is suppose to be an open adoption we have court order visitations phone,letters ex as well as our daughter does , she lost custody because she kept going back to her abusive husband child service told us that he was abusing her and the boy my daughter said he never touch the boy it was only her but child sevice took her rights anyway.We are not in the best health and were not aloud to get him .We have had visits with him with child sevice with our daughter . We all had a week-end visit with him at our home . Our daughter was not there with us yet she was at work . Our grandson had an accident in his pants I took him to the bathroom too clean him up ,he ask me if I was going to spank him I told him no that he had an accident and it was not his fault ,about 1/2 hr to 45 mins later he had another accident I again took him to the bathroom too clean him up he was freaking out begging me not to spank him holding his bottom and the fear on his little face was heartbreaking my husband his grandpa had to come in an help me calm him down . I finsh cleaning him up .I asked him if he gets spanked at home and he said yes I asked him who spanks him he told his grandpa and I his foster brother spanks him he is 16 I asked him why is he spanking you and he told us ( Because he is my big brother ) I told him that he had no right to spank him ,I asked if the foster/adopted mother knew that the her son the foster/adopted brother was spanking him he said yes and she told him to stop . I turned her in to child services and now she has stopped our phone visits with the child was I wrong in do that or should we fight to get the child out of there child sevice has heard this out cry from him before when we had a visit with him at the department of child services he told us that that punk has been spanking him and being mean to him all they done was made my husband an I leave and let our daughter stay because my husband aske the little boy why was that 16 yr old spanking and being mean to him next thing we knew the case worker came in an told us to leave and right before that the child sevice supervizer told us we had a 2 hr visit with our daughter we told the caseworker that her supervizer told us we all could visit for two hours the caseworker said well she just called and ur visit was just to be for a 1/2 hr I don't trust the child sevice in that state so i call the hotline