I’ve heard some coaches say that you must develop velocity and when you get near what would be considered fast for that age, then you work on control. Taking the approach of “get them up to speed, then fine tune the location”.
I have also heard from coaches that speed comes with practice and experience so just throw strikes and speed will come later.
Knowing that velocity and control are not mutually exclusive, there is a tendency for younger kids to slow down their pitch in an attempt to be more accurate. If you were starting with an above average player in 10U who is developing his pitching, do you emphasis velocity first or control?