Yes. I'll try to explain it better. It is sometimes important to locate the fastball inside to the lefty and outside to the righty. Right handed fastballs usually have some amount of movement to the right (arm side). This can put the ball in the middle of the plate when you try to locate left side. A straight fastball or a cut fastball will prevent this from happening. A cut fastball is not a very safe pitch for a twelve year old. The bones in your elbow need to develop a bit more. So for now, I would work on developing a four seam fastball that I can rely to be straight. It would be used for left side pitches and elevated pitches. For right side pitches I would work on developing a two seam fastball that would have reliable movement to the right and possibly down. This pitch is good for jamming rightys and having leftys chase it off the plate.
So I think different fastballs are good.
I think you can throw a slightly split fastball as a change up. I have a son who does. However, I think that consistent movement is hard to achieve with this pitch, although sometimes it is very, very good. That is why I would investigate the circle change first as I think consistent movement can be more easily achieved. But you may find it to be different.
Do you have a breaking ball?