I don't have kids myself, but based on the 2-4 year olds in my family I would say that the logical reasoning part would be the challenging bit, not the counting

I don't have kids myself, but based on the 2-4 year olds in my family I would say that the logical reasoning part would be the challenging bit, not the counting of the solutions. I agree of course that marking and counting is strictly more work than marking only, but I disagree that the counting bit is somehow essential to this game.