Flip the cards and find the pairs.
Memory Match is the classic concentration game with a twist: the pairs are not always identical. Depending on the level, a card might pair with its written word, with a group of that many objects, with a word that rhymes with it, or with a sum that equals it. That turns pure visual memory into memory plus a small piece of reasoning.
The 2-4 level uses four pairs of large cards, mostly identical pictures with a few counting pairs. Four pairs is about the limit of what most children this age can hold in mind at once.