Hey! We have some 4 leaf clover/shamrock novelty glasses that fold along the thin seams, for St. Patrick's Day. They use only a small amount of filament and print relatively quickly.
Print in PLA, PLA+, or PETG. (Yes the seam is thin enough to fold PLA.)
Two different models. Neither are your standard design and are redesigned for strength but decreased filament and print time.
The original model requires a medium or larger printer, as bed size will need to be at least 305mm wide to print at diagonal, or scale model X and Y (but not thickness). It has full size temple pieces / earpieces.
There is a second model that I made so my kids could wear them. The temple pieces are abridged with holes for elastic/yarn/thread/string. These should print on some smaller printers so may be preferable for that reason. I did not make a version where the full size temples attach to the frames because this is likely more comfortable. However, note that the actual eyepieces are not smaller.
They are absolutely scalable for kids with your slicer, but do not scale the thickness.
I'll say it again. The models are scalable in the X and Y directions, but not the Z (thickness). The area that folds is 0.40mm thick for a reason.
You can choose from two different thickness models, the 0.8mm and 1.2mm versions. If you want in between, grab the 1.2mm version and cut part of the thickness off with the slicer.
When folding, I recommend that you fold into the kerf/seam, but don't fret if you mistakenly fold the other way. However, if you keep folding it back and forth, you will eventually break it.