Go on a beach hunt and collect two of anything you can find – two cockle shells, two big pebbles, two seaweed strands. Divide these up between you and your toddler, so you each have one of everything. Draw a line in the sand, then get her to choose one of her treasures and place it on her side of the line. Find your matching treasure, and place it in a symmetrical position on the other side of the line. Once she’s got the idea, you go first and see if she can do the matching.