Use the "Balloon-in-a-Balloon" technique to show children how yellow and blue make green and red and blue make purple.
1. Take two balloons of contrasting colors. The second balloon should be the more translucent for the best effect.
2. Roll the first one long ways and feed it into the second, but leave the neck sticking out.
3. Slide both balloon necks over the helium tank's tilt nozzle (one inside the other) and inflate to about 6 inches.
4. Remove the balloons from the valve and tie off only the inner balloon.
Push the knot over to the side and place only the neck of the outer
balloon over the helium tank's tilt nozzle and inflate to about 9
6. Remove the balloons from the valve and tie off the outer balloon.