The thing is the kid gives back the money he stole with an interest. The thing here is returning the money. As a parent, a simple theft can be forgiven, and forgiving does not condone the action but rather giving the kids another chance, plus the fact that the kid returned the money means he knows his mistakes and wants to correct them by returning the money.
If the kid won the money from the gambling site,he will return your money with the interest.But if he had loss the money in the gambling site,it will cause him to hide their loss to you.They also don’t let you know their stealing money,the parents should take responsibility and give their children some pocket money to avoid of such stealing in the gambling site.
So what do you want to do with the kid? jail them or beat them up because they stole a small amount of your money? I think that is a harsh thing to do as a parent. Reminding/scolding them that stealing is not a good act is enough. Besides, if you beat up your kid as a parent, you will be charged with child abuse, and that makes the scenario worse.
Such violence should not be done against the small kid,instead you can teach them their mistake.Because the mistake was made by the less knowledge of it was a mistake at the younger age.The parents should take responsibility to teach him at the younger age to avoid of the repetition in the future.Because the kids will make this as habit,if you fail to point his mistake at the young age.