If my child won a huge jackpot, then by all means he can use my personal ID in order to pass the required KYC verifaction.
While this may be the case here, as a parent also, I would definitely take measures in order for this kind of event to never happen again. Additionally, knowing that my underage child engages into gambling, such measures would be focused on remedying this kind of problem as this would cause more financial distress on his part if this becomes his habit in the long run.
In conclusion, while winning a huge jackpot by my underage child is a big win for the whole family, the problem here would be preventing my child to avoid engaging into gambling regularly for his own benefit and welfare.