If you have 12u pitchers learning to throw 4 pitchers and they don't have command of a basic fastball (with good internal rotation and a 12/6 spin) then you're setting them up for failure.
I fail to see the logic in denying them the 3 extra pitches. The 3 extra pitches are not going to stop them from controlling a fastball. Plus, 12U ball means nothing. This kid could end up being the best drop ball pitcher in the state.