Petanque.

You can definitely use open courts at parks such as at the Luxembourg Gardens. The simple rules found online are easy for family play. Serious players have more strategies and fine points to the rules.

Just realise that buying a set will add to your luggage weight. Those balls are heavy for their size.

Good souvenir though.

Just an idea ... if you son goes and hangs around where people are playing pétanque, might some of the old guys invite him to play with them? That would be an experience he'd never forget. I don't know if it's like chess, where pickup games in parks are popular ... but it might be an idea, especially in a quieter place off the beaten tourist track ...

Just realise that buying a set will add to your luggage weight. Those balls are heavy for their size.

I can attest to that. I got a set as a gift once, and they really are heavy.

I like the suggestion that your son hang around watching a boule game and acting interested. He might very well get invited to play.

I'm not sure what you mean by
- buy an "experience".
Is this something like a guided tour where someone explains the rules and plays a game of pétanque with your son? If so, and he is keen to experience it, I would encourage you to do this. My experience suggests that he will not be invited to play with those already playing in a park.
I've watched people playing pétanque in Paris and as a kid I watched a fair amount of bocce (a similar game) being playing in my Italian-American neighborhood. In both cases it was my impression that these games are taken quite seriously by the players and none of them would invite a bystander to join in.
Of course, I don't know what would happen if you tried this approach, I'd just hate to see your son disappointed if there's a sure-fire alternative (such as buying an experience).

Just to add another comment. Many towns in France have a "boulodrome." It's usually a large, enclosed area, often along with some outside areas to play, that is dedicated to serious playing of pétanque (or boules, as it is sometimes called). You generally can find them on the outskirts of towns, with the parking lots filled one or two days a week when the matches are played.

Stay away from those.

What would work better for you would be to find some casual pétanque playing areas in a city park. There, you might be more likely to find some guys who are just relaxing with a few games and who might be more willing to give a young sprout from the U.S. a hand at trying the game out.

Thanks for all of the advice. I love love love the idea of a pick up game with locals. We are staying in the 15th so it’s. It exactly tourist central. A friend of mine sent me to a link with a video about pétanque at the Paris Plage. Looks like a lot of fun. I don’t think I’m going to buy the experience (like a tour). If we end up buying a pétanque set I don’t think I would bring it home since they are heavy.

Thanks for the advice!

Paris Plage is probably the right setting for a pick up game. Here's a video that seems to show a class for beginners
https://www.youtube.com/watch?v=cLN7EHR0PjU

Will you be there during Paris Plages? We played there a few years ago! The lady giving out the equipment did not speak English at all, but I told my son (about 11 at the time) to just watch everyone in front of us for what to do to pick up the equipment! It was one of my favorite memories because she was telling us which court to go to and held up five fingers and kept saying "six"! I was like "five?" and counted it out. We all laughed, it was super fun!

Kim, Paris Plages sounds so fun! What a great experience you had.

And Bob, I love that video. The lady says it is for everyone, all ages, men, women, French, foreigners/tourists .... and it is free! So cool. It sounded like (in 2011) there were two venues, one on the banks of the Seine and one at the Basin de la Villette. I will have to check out Paris Plages someday.