I used the size of the biggest books and the size of my kid to determine the size of the bags. Truthfully, they could have been a little wider, but I wanted the books to fit snugly so everything would fit neatly, and I worried about a shoulder bag being too cumbersome on a little shoulder. Then I got to the hardest part - fabric decisions!
I needed a way to package the crayons and pencils. As you can almost see above, I went with crayon rolls! (And modified the dimensions to make pencil rolls, too.)
So each kid will get their own tote bag (technically reversible, but it does have an outer pocket) filled with a coordinating crayon roll, a coordinating colored pencil roll, and a bunch of books to use them in!
I'm not going to lie, it was a lot of work. But doing them all at the same time helped, and I'm happy with how they turned out, M is excited to give them to his friends, and hopefully their parents will be as relieved as I would be to not have to add another toy to the pile!