I don’t think the mother is mad about her son gambling, just the way he got the money. Stealing is a crime and if unchecked he could develop a habit for it and steal from someone who is not as sentimental and would very well call the cops. I think the mother is trying to prevent such an occurrence from happening in the future, the OP doesn’t say the age of the boy, I can only assume he’s a teenager. The family should have a sit down with the boy and let him know the consequences of his actions.