Many of you probably learned a bit from the How and Why Wonder Book series:
These were produced in the US during the 1960’s and covered many subjects in science, technology, nature and history. They were large format books of 270x205mm, mostly softcover, but hardcover was also available. They are always 48 pages long, and mostly illustrated with simple painted artwork, though some photographs are used. The books are structured into chapters based on sub-topics of the title subject, and within these are questions that a child might ask, followed by a half page answer to the question.Rob Storey has collected most of the covers.
Via Reflections in d minor.