Does the Government monitor parents spending on SSI money for ADHD child?

My brother lives in WISCONSIN and he and his fine wife recently have recently $700 a month for SSI regarding their ADHD 8 yr old son. My bro told me they use the money to make their house payment. Is this illegal since they should be using it for their son and it is technically HIS money for his disability? Is seems to be improper use of Government money.