My mother used to make these all the time when I was growing up.
1 pkg Jello (3 oz)
1 pkg Kool-Aid
1 c sugar
2 c boiling water
2 c cold water
Dissolve Jello, Kool-Aid and sugar in boiling water. Stir in cold water. Pour into molds. Place filled molds in freezer and wait 2-3 hours until set.
My favorite flavor then and now is black cherry, though strawberry-banana is pretty good.