If the events recounted in the many Magic School Bus picture books actually happened, most people would die of fear or chalk them up to hallucinations. Ms. Frizzle takes her public school students on adventures throughout the natural world in a school bus that can fly, shrink or whatever to go into outer space, molecules, etc. The adventures are entertaining and the scientific content is surprisingly educational (though some parents will want to know the series is written from an evolutionary/humanist standpoint). The number of books in the series is apparently interminable, but they are short and fast reads so your kids can be briefed for a variety of science subjects in a matter of a couple hours.
Ten original titles and many spinoffs: