One thing I’ve learned after years of pro DMing for kids and grownups is that they learn the rules of D&D at almost the exact same rate.

In any case, I suggest to parents who want to introduce their kids to the game not to start by watering down the rules. You don’t have to overwhelm them with ALL of the rules in the beginning (that’s not really how you teach anyone to do anything) but don’t avoid complexity for its own sake.

But it’s that complexity that makes it fun. Two players in the same game can be enjoying it for totally different reasons. One may enjoy the role playing. Another might be figuring out cool combos.

Plus, age really doesn’t matter much. I’ve played with grownups for years who still need reminders for how the same rules work all the time. I also play with 9 year olds who know the rules better than I do. Some pick up on the rules. Some don’t. It’s a complicated game.

I get the impulse of wanting to lighten the cognitive load of D&D for kids, but you’re also skipping many of its benefits. Reading comprehension, math, and probability are all available for them to grasp in a cool context that doesn’t have to feel like learning (but totally is learning).

I see a lot of parents assuming they need to water down the rules for kids. That may be true if they’re not getting into reading yet, but the kids in my program start at about 9 and are mostly reading by then. I started playing at that age myself and remember the tiny text of the 1E books.