Step 1: Gather a tall, large box or carton from your local grocery store or appliance store so that your child can stand up while painting on the box surface. Purchase a small paint brush (½" – 1") like one that may be used for window trim; it has a short wide handle that will be easier for little hands to manipulate and make marks that are easy to see. A small paint roller also works well.
Step 2: Find a container that will be easy to dip the paint brush or roller into, like a toy sand bucket or a plastic container. Take everything outside and add water to the bucket.
Step 3: If needed, demonstrate how to dip the brush or roller in the water and paint the box. Let your child go for it!
Step 4: Comment on what you see your child doing, talking to her about the marks she is making on the box or asking questions to engage her in conversation. Observe and comment on what happens to the water marks as time goes by (e.g., they disappear as they dry), or what happens to the box as it gets wet (e.g., it looks darker). You may even want to grab a spare brush and join in the fun!