We have covered a bunch of awesome 3D printers in the past. Not all of them are suitable for kids though. The XYZprinting da Vinci miniMaker is different. It is a lightweight 3D printer with a build volume of 5.9 x 5.9 x 5.9 inches and non-heated print bed for child safety. With XYZmaker, you can design your own 3D objects.
miniMaker features auto-calibration and a max speed of up to 100mm/second. The unit weighs only 18lbs. Plenty of educational resources will be available to owners. Costs under $230 at this time.