3D printing is a perfect match for lightweight prosthetics, it turns out. The material makes so much sense for children, whose parts will invariably need to be re-sized and whose use of force is still in development. I covered the "magic arms" a few months ago; the promise of these printed parts' physical qualities, plus resources like openSCAD, just keeps getting better. The designer-engineers just made the project entirely open-source over at Thingiverse.
The video below tracks Liam on Day 3 of his new hand's use—practicing the fine art of picking up coins from a table and throwing a ball.
More videos and documents of this collaborative project at Coming Up Shorthanded—see photos below documenting the progress of the finger designs—and some great background at Ars Technica. (Thanks, Khairani.)