One of the benefits of being married to a teacher is that fellow teachers are always getting rid of interesting things. One of those was a bag of 2 x 2 blocks that had been cut from a strip of lumber (yay for free stuff!). None of them were exactly square, but that didn't matter much. In fact, almost any wood scraps will work, so check your garage or the scrap bin at your local hardware store. Then I bought a package of large foam tangrams from the dollar bin at Target. I like the smaller pieces rather than a sheet of foam since they can be held and cut more easily. After opening the package, I let Goen loose on the shapes with a pair of scissors (setting aside a couple for myself to cut more specific designs). He happily cut away while I used plain white glue to attach the shapes he cut onto the wood blocks. Most of the pieces he cut were completely random triangles and quadrilaterals, but I placed them on the blocks to make interesting patterns. I even pulled out my hole punches and punched holes in the foam to make dots and "negative space" dots. Cutting stripes and curves created interesting designs, but my favorite was cutting spikes and chevrons. I will say that the foam is hard to cut in a curve with regular scissors, so don't expect to make intricate designs. Another fun thing is to use a pointed tool to etch into the surface of the foam. You can get way more detailed here than with cutting.
I did two stamps on each block to maximize the number we could make, though you could probably do them on more sides if you don't go all the way to the edges like I did on many of them. There were so many foam pieces that it actually took us several days to glue them all (in fact, we ran out of blocks before we used all the foam). By the third day of stamp-making, Goen was actually gluing pieces right alongside me. After the glue was dry, we used do-a-dot paint markers to ink the stamps. There are pros and cons to the paint markers, of course. Lots of paint comes out so it inks the foam quicker than an ink pad, but it can also glob around the edges and prevent perfect impressions. Also, rubbing the paint marker across the foam shapes roughed up the sponge tip quite a bit. However, considering that I was doing this as a kid-friendly craft, I think I would still go with paint markers and get out the ink pads when the kid is in bed.
The toughest part for me was staying "hands off" and letting him do the inking and stamping (and gluing) by himself. It's not about making it "perfect." Lay a sheet or towel down if you're worried about a mess. But, really, the best thing is to just make sure you use washable paint or ink. Oh, and one other tip. Don't tell your kid not to paint on themselves. I tried that and it just caused him to "hide" on the carpet next to his chair where he was far more likely to make a mess on the floor and walls than if he was at the table painting his hands. Tables are easy to clean, walls and carpet are not.
I had so much fun making and using these stamps. I made repeating patterns by rotating the blocks to see how they would look. Some of them were so interesting that I want to digitize them and design some fabric through Spoonflower. I've already got my impressions made. I'll let you know how it turns out. In the meantime, get stamping!