~ The proper guidance of the parents about gambling can help them to better understand its risk and what it can do to a person if they let themselves be hooked at an early age.
It's pretty hard to explain all that to kids at an early age. So, I would suggest to wait until they are 12 at least. Until then they just shouldn't be anywhere close to gambling same as they shouldn't be anywhere close to many other things that can dangerous to approach at their age. Also, you can't be an addicted gambler and give your kids a proper guidance regarding gambling. Let's establish that.