Gonna go ahead and add another “No” to My Hero Academia. The violence in that show is a step or two worse than Avatar. I’d probably wait until age 10-12.
Little Witch Academia and Digimon are great recommendations.
Along similar lines definitely check out Summer Wars and Dennou Coil. Summer Wars is a great film for anyone who likes Ghibli stuff. Dennou Coil is a cute, beautiful, funny, and melancholy series about middle school hacker detective kids with AR glasses.
Maybe Last Exile, too. It’s basically Steampunk Anime Star Wars. But the pacing might be a bit slow for a kid.
Avatar is also inspired by lots of classic shonen anime, which might be worth checking out. Dragon Ball, Pokemon, Yugioh, etc. Where to start in each of those series could be an entire separate thread…