Incredible Cross Sections (from 1992) is a great book for the curious child who asks "what does it look like inside?"  Whether it's a castle, coal mine, tank, helicopter, the space shuttle or a host of other things, all is revealed with the incredibly detailed drawings.

The Children's Encyclopedia covers 130 major subjects, more than 700 entries with 750+ drawings.  This would be a great resource for a first research paper.