The subject that I know most is chess. Because it requires high intelligence, from the age of 4 my parents let me make it up. The rules of the game are also quite simple. Putting the chess pieces together, the chess pieces are aligned with the queen. And the others are aligned. The first pawn can move 2 steps, the other can only move one. The knight moves straight and horizontally, the flat pieces go diagonal. The king is only allowed to take one step, but he can go left, right, horizontal and vertical. My favorite is the queen, you can go as much as you like. The rules are very gentle: move one to take the other. But it takes mind to move the pieces in the right direction. Nowadays, chess is very popular among children.