I'd like to think that understanding how the brain responds to gambling, why the games are designed the way they are and how exploitative the companies behind them are being can help, but I wouldn't expect a child to be able to really grasp all that well enough.
You don't learn that gambling is bad by gambling a little bit and losing a bit of money.
If people were rational enough for that, people wouldn't suffer from gambling addiction.
There's only one way to protect kids from gambling: don't let them get near it.