Blocking in app purchases in arcade

I am actually trying to stop my grandchildren from buying “lives” on the arcade games on the Apple TV’s.

I have several apple TVs, iPads, iPhones, iPods and my whole family and descendants are ALL apple people!

I am an old grandma, and I feel like I’m unable to keep up with all technologies.

In the past years, I may have accidentally overpaid Apple a few THOUSAND? US dollars, due to my own ignorance and embarrassment to call you for ever having spent money in-app purchases.

All I need is to learn a simple way to block them, and outsmart the little grandchildren that don’t understand (like me) that they’re incurring charges.