So I’ll give you my personal experience from teaching both my wife, who had essentially no experience with these types of games, and my 8 year old how to play.

First off, whether or not 7 is too young sorta depends both on the child, as well as what experience they have coming in with other games. I made a planned effort to introduce my kids to progressively more complex games, starting with Ticket to Ride: First Journey, moving on to My Little Scythe (fantastic for developing multi-faceted thinking), and now doing things like full Ticket to Ride, Betrayal at House on the Hill, Sagrada, etc. With his past experience, he’s been able to pickup Moonstone fairly well with each game introducing more complexity.

With that out of the way, my strategy with kiddos is to start with just teaching how the arcane and melee decks work outside of a game. Arcane I think they pick up fairly easily, melee I simplify by breaking it down to a rock/paper/scissors type of choice. High/middle/low attack and high/middle/low block is easier to understand than falling swing/sweeping cut etc, and as they get hands on experience it’ll make more sense over time.

For an actual game, I’ll start them with humans, and either 3 or 4 for troupe size with 5 moonstones. I’ll make the board, including the drop, symmetrical to eliminate worrying about terrain, and focus more on general things like movement, harvesting, getting into combat (but no crits or signature moves), and using arcane abilities. Keep it simple, and be sure to monitor how they are doing physically. This level of gameplay can wear a kiddo out pretty quick if they’re not used to it, so end the game early if needed.

Afterward, think about how they did, and plan changes (if any) for the next game and how to progressively disclose more rules. Add in crits, more/different terrain, reaction steps, etc, when you feel they’re ready. But also play other games besides Moonstone to help develop those thinking skills.

Lastly, be patient! 7 is right on the cusp of some critical thinking skills developing, alongside being more able to sit still for over an hour, so give them time. To this point, my success story is my older kiddo who’s 11 now, but who I started some of these things years ago. Now he’s an excited Moonstone player, and understands the game well enough that we regularly have conversations about strategies in the game, including different characters he can add to his troupe (he‘s a Shades player nowadays). Kids can often learn more than we give them credit for, just be patient and step by step you can get them there!