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shot in the dark but Stickin' Around has a black boy and a girl in a wheelchair (though the latter is a secondary character) with hyperactive imaginations
Back in France we had this
. The screenshots on the right show three characters fitting your descriptions.
Aye, same. I couldn't even find the English version anywhere, and the few available videos of it online only consist of the intro in French and Portuguese, and two Portuguese dubbed episodes... all in home-made recorded quality. It's a shame the creators didn't archive the show. I would've bought a DVD/Blue-ray release in a heartbeat.

I don't know if this show was made in the 1990s but that's the time I remember watching it as a kid. Memory's vague but the art style somewhat reminded me of Peanuts and I recall a few of the main characters consisting of a tall black boy wearing a red sweater, a rather sassy girl in a wheelchair wearing a purple dress, and a young, bespectacled blonde woman who was their teacher. I can barely recall most of it but I remember this one episode where one of the hyper-imaginative kids got so into the idea that he's some kind of superhero that other kids started to follow suit, and the opposing kids forming their own "anti-superhero" team by dressing up as humanoid mutant alligators. They almost get into a rough playground fight until their teacher dresses herself as an amalgamation of a superhero and a mutant alligator, calls herself their "god", and essentially gets them all to calm down by imparting a lesson about getting along and settling differences peacefully.
I don't recall their accents but it was definitely not American, sounding either British or Australian. Asking here because I tried to google it based on these few memories and had no luck so far.
Edited by 9thOutworldsMan