What about salt dough? It's very basic, maybe too much so but might be a good starting point?

I use 1 cup of flour, 1 cup of sugar, 1/2 a cup of water or you can do 1 cup flour, 1 cup water, 1/2 cup salt.

Then you get to play with it after

ETA - just thought, you could also use it for measurements, like get him to cut 1cm pieces etc?