but let's just imagine that this boy won millions of dollars with his school fees, do you think he will get paid? Even if his parent knew about it there is nothing they can do to get the money out, the boy is underage is going to be the excuse anyway.
The casino can only claim the excuse of underage and further stated explicitly that winnings from underaged are not redeemable, otherwise if not stated about the ban of underage gambling from their platform in their ToS it will be difficult for them not to pay the boy. If that is not written their in the ToS, the parents will claim the winning for the boy by contacting a lawyer that will file a court action to prosecute the matter.
But even though the child's parents will sue the casino because they refuse to pay the child's winnings on the grounds that they did not write down the prohibition in the ToS, it seems like it will only be in vain because the casino will usually always win when in court because the casino will also use reliable lawyers and have many money to solve the problem.
However, if the parents threaten to take action in court, it seems to depend on the law in the country whether minors can gamble and if the state law says minors are prohibited from gambling, I think the parents' efforts will be in vain.