One team we played had their pitcher throw nothing but CB's to our top six hitters. He threw ONLY CB's. He threw 116 pitches in 5 innings and at least 70%-80% CB's.
His dad is the head coach. After the game I asked him why in the world would he let his son throw that long and throw so many CB's. He said that the odds of his son making it to MLB is 1-in-a-million so why not let him have fun now.
We have 4 pitchers on this team and we have taught them all (with parent's permission) how to throw a CB properly. We call their pitches in the game and we call very few if any CB's. We emphasize the use of location with the FB and a CU. We will call an occasional CB just to show it but never more than once or twice an inning.
I agree with Fungo that the boys should be taught how to throw a CB so that they don't hurt their arms. Parents that tell their sons to not throw CB's are too often surprised to learn that they still do regardless.