You will need:
3 small bowls
Red, blue and yellow food coloring
Flower shaped tray (I got ours from Hobby Lobby for $2)
An eye dropper
What to do:
Put some water in each of the three small bowls and add 2-3 drops of food coloring to each one. Encourage your child to mix the colors using the eye dropper and make each petal a different color.
This project kept my 3 1/2 year old busy for at least 40 minutes, we would dump one "flower" out and she would fill them again and again with different variations of each color. We added in some plain water at one point to make a more pastel looking flower. Have fun!