For some reason, some kids just read on stage as adults. You'll recognize this quality by comparing kids. Since THE MUSIC MAN JR. is about a town, you'll want to assign your cast into family units. Try to create a realistic town with married folks, single folks, etc. If you have an abundance of girls, cast a few as widows. Ask each family to create a family history, including details of their lives. By doing this you will create an ensemble that is engaged and energized and this will greatly add to the quality of your production! The adults have a few lines (which you can distribute while blocking the scenes.) They also have some solo vocal lines. You'll also want to select the Farmer and His Wife from this group.