Octagonal construction toy set, build all sorts of objects with simple interlocking octagonal shapes. Easy to print and guaranteed* to keep your kids entertained for hours.
Octagons are 50mm (2 inches) across, so shouldn't be a choking hazard (don't take my word for it though) - and there is a print profile for 50% scale for 25mm (1 inch) octagons.
The print is very simple and should work on any printer. I've printed a few plates in different colours, and my kid loves it. We've made robots, and dinosaurs, and bridges, and balls.
*unless they don't like it. :-)
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