Social Security Survivor Benifits?

I have recently gotten guardianship of my nephew who receives survivor benefits from his dad passing. My question is that the mother said that she would just send me the benefits when she received them, but it has been 3 months and nothing. I am not looking for the benefits to benefit me, but they should go to the child. I am financially caring for him and would rather see the money put to better use like setting up a college fund for him. But I can't see his mom keeping them and spending them on herself. Is there anything that can be done?