I suggest browsing the science books in the adult section of your local public library. I was doing so yesterday and noticed that many of the science books are for the lay reader and do not assume much of a math or science background, so they may be suitable for students in elementary or middle school. They are not college-level science textbooks.

The adult math section had several Life of Fred math books that we had not bought yet. My son was excited when he saw them.

"To see what is in front of one's nose needs a constant struggle." - George Orwell