A good diagram of a camera for a primary student to use for a project to explain its use

The best resource for this is a good old-fashioned book (remember those?).

Most public libraries, book stores and many camera shops have a few titles along the lines of "photography for beginners" with a large assortment of diagrams. Some of the books are even pitched specifically at children.

Searching online is OK, but the information on the internet is only the tip of the iceberg compared to what else is around. Many of the best diagrams and publications pre-date the internet age and so have never been scanned to web.

Have you tried Wikipedia?