Use watercolors or make your own by adding several drops of food coloring to a small glass of water and stirring. Make several colors so your child can make choices.
Let your child paint colors with a brush on any type of paper.
Give your child a little salt in a small bowl to sprinkle over the paint
Watch the effect.
If you have a bottle of glue, let your child drizzle it on top too.
Talk about colors and what you see
Keep experimenting until your child is done.
Let the art dry, then hang it on the refrigerator and talk about it more.