The saddest thing I have ever saw

I have made a few posts in the past about me being a foster parent. This was honestly the saddest thing I ever saw. My foster son has been trying to have visitation with his mom, but she kept missing or rescheduling them. She missed his birthday and was supposed to make it up to him with a visitation yesterday. So he got dressed and my husband drove him to his visitation. It would be the first time he saw his mom is 8 months. When they get home I ask how it went and he just said "She didn't come." And went to his room. He has locked himself in his room all day. He will not come out. It was really sad. I tried to give him a birthday present but he doesn't want it and just wants to be left alone. Any advice on how to make things better? I think right now he may just need his space.