I don't know if it's really up to you to say anything to the mum. There could be so many things going on in their lives that you have no idea about... Whilst your "gut" might be right, if it's not and the mum listens to you, things could seriously go pear shaped and the boy may not get the help he needs.

Maybe just be there as a friend to the mum if that's your relationship.

Goodluck!