Watch Spirited Away, Princess Mononoke, Grave of the Fireflies, and Millennium Actress, then report back to me on the intelligence of anime.
My kids are also so into anime. They started with Pokemon, which really is far more than the TV show; the Pokemon fantasy world of the Game Boy games is complex and involves math and logic skills, implores kindness and consideration, and is so multifaceted that if your seven year old does not have one of those games, you should run to buy one for him.
Anime is THE big thing for smart kids, usually males, to enjoy these days, and as long as it's G-rated, it celebrates intelligence, is creative, and is not as formulaic in plot as the boring American fare like Scooby Doo.