The SSA require that Social Security benefits be used for the person that is eligible to receive them and in some instances for a dependent spouse and minor children.
SS benefits for minors are due to the loss of a parent 'survivor benefits'.
The general criteria is that such monies are to be used for basic necessities, food, clothing, shelter, education, in some cases a reasonable amount of spending money for an older child, etc. with any remainder placed in a savings account for the minor child.
It would be extremely difficult to prove that benefits for a minor are being misused unless an investigation by a social service agency or other authority proved that said minor child was living in an unsuitable environment and had been subjected to neglect and/or abuse.