Very cool! Planning, executing and then getting to use something one made is a great feeling and cool for kids! Are you recycling plastics into filament or can you buy it recycled?
I bought a few spools from a company called printerior. It appears they recycle pla and other types and make it into filament. I have a box of my waste pla I'm about to send to them, just don't have enough yet to justify it.
So far their filament is fine to work with, a tad stringy, but nothing major.
Cool. How old was your kid when they could start using the design program well? It never occurred to me in all the years I've known about and decided I didn't want a 3d printer that I could make stuff with the kids.