Zip ties are generally one size fits all. How young of a boy are we talking about?

Also, making this is about as easy of a craft project as there is. You need probably 100 stones, some E-6000, and a wax tipped application tool. You put a small dot of glue on, then push the stone on, and repeat until finished. Don't worry too much if it looks a little funny close up, it'll look great on the dance floor under the lights.