Here is the perfect set of melody bells to keep your students occupied while some are playing and others are not. Let them practice on paper bells! This paper has both note names and color coding. Choose whichever is easier for your students to use. I keep a class set in plastic sleeves in a three ring binder.
I tell my students if they don't practice on the paper bells, they won't know what to do on the real ones. You will also find that the last group to go, if they practiced, will do really well with your song. Exciting!