Legal Question in Business Law in California

Sounds like the elements for a classic case of fraud are present, assuming your son had little or no knowledge of what was going on. Until a child reaches the age of 18, parents do have certain rights regarding the property and worldly affairs of their children, but even then the mom's actions would be dubious. Within a family, I'm not sure ho you'd want to work this out, but I'd say if the son wasn't aware of what was going on, and genuinely thought that mom was paying for his education, he'd have a strong case in court.

Is this a valid contract?

Not if he is 'innocent' of knowledge and participation in the loan.

If he took and used checks from the govt, he is not going to avoid the debt. Even if he got checks from the mother after she illegally and secretly deposited the govt checks in her accounts, as far as the 'innocent' govt is concerned, he made the loan and they will seek to enforce and collect it. There is no 'easy out' here for him, and anything he does to fight it will incur substantial legal fees. He could sue the mother on various theories if he is willing to seek the money from her.

Using someone else's, even a family member's, social security number to obtain credit without their consent is identity theft and is a crime. Typically, student loans are disbursed through the school and the student has to sign to receive the money or have it applied to his tuition. It is therefore implausible that he didn't have any idea that loans were involved. The question now is whether he or his mother is going to take responsibility for paying them back. If she promised to take care of his education expenses, perhaps she meant to pay back the loans herself.

If he wishes to challenge the loans, the first step would be to ask the lender for copies of the applications, then see an attorney for next steps.