As I go thru the link I found this on the details of Wiki.
Children aged five are permitted in casinos. That is because the younger children (babies) do not know the meaning of money.
Somehow it is a good explanation.
Parents won't give them money since they know nothing about it.
How could they bet on something if they don't know the purpose of money or they don't even have the right amount?
But when the kid goes 8-15 years old then he knows it.
That means they could gamble their way if they have the amount needed.
There is also a chance they will make that money with bad ways.
There is worse than this.
Gabon - There is no official gambling age, although many incorrectly believe it to be 18.
True... They don't know the meaning of money. But neither does a 3-year old kid and yet he is forbidden to be in a casino. That's why I think it is a stupid rule. Either way, I think that any underage person have nothing to do in a casino.