You will need:
Acrylic paint in red, yellow, and blue
A few paint brushes
A cup half-filled with water
Large piece of paper
Squirt a bit of red, yellow, and blue paints on a paper plate. Let your child mix a little red paint with a little yellow paint to create orange. Then, blue with yellow to create green. Next, red with blue to create purple. They can experiment with different tones (a bit more red here, a bit less yellow there...)
Next, let them paint their color creations on a color wheel on a large piece of paper. After the paint dries, you can play scavenger hunt in the house to find small objects that mirror the colors on the color wheel. Place the objects on the color wheel, so that the colors correspond.