Think about buying or building your kid one of these. It's an open source 3D printer. I bought mine from BitsfromBytes in the UK for about $1,200, mostly because I was in a hurry. You can build your own for maybe a third of that.
You can either buy the controlling electronics off-the-shelf.
... or ... if you want to get your kids into electronics, you can build up your own like I do at times. I tend to use stripboard for circuitry. You can get stripboards cheap out of New Jersey.
I use DIP though-the-hole chips because I'm old and clumsy. Little fingers can handle them a lot easier than you can with surface mount chips and components. I put together a layout app for design.
That makes getting from concept to board a lot easier.
Once you have your 3D printer working you can get your kids going designing and building THINGS instead of sketching things on paper or on some 3D CAD program.
I think there is a lot of potential for getting kids used to thinking in terms of solid objects and how things go together. One of the immediate applications is for kids to design and build their own robots. Robots tend to be team efforts at the kid level largely because there are parts that are expensive to make because you either have to have a machine shop or access to one. With a 3D printer you can simply print the fiddly bits.