It depends on the casino, but it is customary for money not to be returned to those who lose their bets, it doesn't matter if the bettor is a minor or an adult, what is certain is that a loss is still money lost, If the casino returns the money, it is dangerous, it could be infected again by those who have the same fate as the child, the parents will also demand the same thing.

Question: what if the child gambles and they win, the parents will be happy, will the casino ask for the winnings again, of course not.

In fact, in cases like what happened to this child, the ones who should be blamed are their parents and the casino.
1. Parents do not supervise their children in gambling activities, they should control their children.
2. The casino is also guilty of allowing underage children to gamble there.

This must be blamed on both parties, demanding the money back is not an option, parents should be a valuable lesson in this case in the future where they really deal with their child's activities, the same goes for the casino, minors are not allowed to enter.

In my opinion, the child was not betting for the first time, perhaps it was the umpteenth time, perhaps that day by chance bad luck happened to the child.