With the best will in the world, I really don't think a Cannondale frame (coke can) would be a good idea for a seven year old even if you could find on the right size. :? Just think back to what was important to you when you were seven, I know what I used to do to me bikes and anything other than bullet proof just wouldn't have cut it.
The Zaskar idea is a better one, but I agree about a 9 year old needing 24" wheels, my lad is 9 and there's no way a 26" would work for him.