How would you like to try Zip Ties for binding your booklets? They are very cheap and come in a multitude of colors. The trick to using zip ties is to put a large marker between the booklet and the tie when you zip it closed. That way it makes a circle and gives room for turning the pages of the books.
Kids love a new trick.
A different method would be to bind the booklet by one top hole and secure with a brad.
Try using string put through the holes and wrapped around a marker and tying.
The more traditional are binding rings that can be found at any craft or department store. Or coil bindings that can be found at any Office supply store. Take your pages and they will punch holes for you.
To make a template to align the punching holes, cut a 1/2 inch (7mm) strip 6 inches (15.2 cm) long.
Fold in half and crease, punch a hole in the center of the fold line.
Fold each end to the middle, crease and punch a hole in the center of each crease line.