L.G.
I have the same problem. I have been seing spirits since I was 3 years old and I am now 30 years old. There is several things he can do. He can tell the ghost that he is seing to go home or go to the other side, or just leave me a lone. If he is seeing them at home too he can sprinkle salt around his room, out side the house, and inside the house. He has a very special gift.
I also suggest that you and him should reas some books by Sylvia Brown. Some of her books really help me. Good Luck.