Clearly, they cannot play at casinos or for real money online. I suppose they could play for fake money online, but there the dynamics are much different. (Why not go all-in and risk it all if you can just create a fresh account if you lose?) Fake money tournaments, where the goal is to come out on top instead of maximize profit, are probably the best option. But the word "tournament" doesn't appear in the article (and even then, is it really good for kids to be hanging around with the people on online poker sites)?
I suppose implicitly the author is talking about playing heads-up against a parent at the dinner table, or with close family members, with fake money. But people who don't know anything about poker are going to play essentially randomly, and the game won't last long enough/will be too variable for the kid to see any reward from playing "correctly," so I'm not sure there's a point.
Also, the first thing to teach the kid is to fold most of their hands. But sitting out of hands is boring and the kid is going to get bored. It's called "grinding" for a reason...
Something like MTG that isn't pay-to-win would be a better choice.