Inkscape and Gimp are free for any use but not without a learning curve. However if you have the computer it is an excellent way to teach the kids basic use of a computer. If the kids can find access somewhere, a library, a friend etc they can learn to work there and bring the work to class by chip (the small ones are very cheap and big enough) or internet if available.
There is probably no more important skill for a child to acquire these days than basic capability with a computer,
Double reinforce the attention needed if doing cardboard, like part of a box. You will want to use at least part of the material that came with the machine to make bed pins You will also want to use a sheet to calibrate the camera and after doing that it is a good material to make into bed pins.