Ethan this is such a great question that everyone asks.  I know you will get specific deetails from readers that have done Peter Pan JR, Willy Wonka or even Drowsy Chaperone. At the Broadway JR level we truly encourage the art of stagecraft. Moving clouds with actors controlling them while John, Wendy & Peter are "flying" on stage boxes.  Many use sky projections and one of the most creative I ever saw was totally student driven- a sky painted screen that rolled up with actors in front. Lighting can also help with the flying effect depending on your equipment.  The most important thing is to remember that your actors at this age and SAFETY are the most important part to tell the story.  Not expensive rigging and mechanical means that make a student feel uncomfortable.