My 5 year old loves to create "books", which to date consisted of stapling a few pages together and going to town on them. Lately he's been interested in "chapter" books with a little more structure: a picture and some text on each page.
He asked for my help in putting one together, so I made a simple template that can be printed out on regular 8×11 paper, folded in half, and stapled to a number of other folded copies to produce a book. Each page has space for a picture, a few lines to write on, and a page number. Here's the template for your enjoyment, in both pdf and svg.
To assemble: print 5 copies. Put 4 of the copies back into the printer such that you can print on the opposite side, and print 4 more copies on them. The page you saved is the cover, and the rest are the inside pages.