You might think sewing too delicate for small hands, but it exactly the kind of meticulous fine motor work that children enjoy, There are many extensions for this kind of work, but as I am not a seamstress myself, I lead my sewing projects towards bookbinding, which is relatively simple.
This can be done with primary students, but is probably ideal for kindergarten and lower elementary.
For older children, I'd recommend using a tutorial like this one from design sponge.
For younger children, a blanket stitch is an excellent goal. As long as the book stays together, I wouldn't worry too much about how pretty the stitches look to start.
Simple Bookbinding
Step 1:
Pick the pages for the inside, and fold them in half.
Step 2:
Mark and poke the holes with an awl or pin-poking tool. Make sure you have thick felt or something else to protect your work surface.
Step 3:
Prep your needle and thread, and stitch
Step 4: Glue insert into cover
Optional: Use tape to recreate the look of a binding.
If you really want to take this project to the next level, have the kids recycle and make the paper for these books!
Paper making is super easy if you have a shredder and blender handy to make the pulp and kits can be purchased from $20 - $50 though a deckle and screen could be made for less.
Next time I get a chance to do papermaking with the kids, I will upload some pictures!