You can check out The Design Team Tutorial Project (aka "The Matrix) for step-by-step instructions for a lot of software packages to help you get to where you want to be.
From your description it sounds like you’re printing out a template and letting the kids design from that? So you have the basic airplane model and they’re decorating it? If that is the case a cell phone and a single vector model might be your best bets.
A bunch of us would be willing to help convert your template file into a vector (SVG) format. If you want to share a picture of one of your student creations we might be able to better help with suggestions also.