You need a set of art postcards, like these. Cut each postcard into pieces. The younger your child is, the less pieces it has to be. A two year old needs 3-4 pieces only. Then, give your child an intact postcard with the painting, say it’s name and the artist’s name and let the child make up this painting, combining the pieces.
This activity teaches your child art appreciation and thinking skills. It’s a lot easier to memorize and study great works of art if the child has to manually put them together. Children notice painting technique and small details this way.