For kids old enough to resist eating clay, you can duplicate the PlayDo Hamantaschen-Folding Practice on a mini scale with polymer or air-dry clay. I vote for polymer as the best choice: you use a tiny amount (which means it is cheap and easy to manipulate), you can pull the colors apart for do-overs, and the smoothy, firm nature of the clay is very forgiving in clumsy little hands. Polymer is also relatively tough when baked, especially when baked in compact shapes like a hamantaschen (as opposed to a wee, polymer lulav).
With polymer and air-dry clay, there is no need to roll out a thin sheet and cut, like with the ever-so-fun PlayDo. Kids can just roll a tiny sphere of clay (in palm or on table), flatten into a disc, place a small dot of “filling” clay in the middle, and then, with help (sometimes a lot of help), fold the edges to form a triangle. Bake the polymer as per package directions, leave the air-dry clay alone for awhile, and you’ve got lots of tiny cookies for Playmobil, LEGO and other figurines / dolls to enjoy.
Don’t have the right color of beige? Blend what you’ve got. Try white with a bit of red, yellow and a smidge of blue. This could be a whole lesson in color wheel and blending.
And, If you wanna do this in a classroom, a toaster oven on the counter works just fine, and the kids can take the clay Hamantaschen home that day.