The Magic School Bus was an awesome and educational show in the mid-nineties, with memorable characters (primarily the Frizz, let's be honest), actual plots, informative episodes, etc. Unsurprisingly, Scholastic didn't release an RPG based on it, because Joss Whedon is the only person who gets rulebooks for his shows published. So this is going to be using an even more simplified version of Fate Accelerated: all you need is a high concept/trouble and the approaches. To be honest, the aspects only really matter insofar as they guide your roleplaying -- there will be no fate points, no dramatic heroics, and generally nothing involving extraordinary people. The characters aren't heroes, just kids exploring the world with an experienced guide and a magical bus.
So: come up with an elementary school student, and a few possible topics for episodes. I'll pick something that seems interesting after some people have posted, and then Ms. Frizzle will start the show. (You can play someone from the show if you like, but obviously not Ms. Frizzle, Liz, or the bus. On the off chance someone wants to be Janet, I highly recommend not portraying her in a bitchy phase.)