Dab the Kool-Aid with a paper towel to remove the excess liquid if the stain is fresh. When the Kool-Aid dries, dab the stain with liquid detergent to pre-treat it.
Dilute all-fabric powdered bleach in a container of water according to the directions on the bleach package. Soak the coat in this diluted bleach solution.
Pour fresh liquid bleach into the container cap and add the bleach to a container filled with water. Soak the stained coat in the liquid bleach until the red stain disappears. This usually takes about 15 minutes. If it does not disappear, add a bit more bleach.
Launder the coat with cold water to remove the detergent and bleach.