I would recommend that you have your fastest girls that can catch anything in the outfield because that is where most of the balls are going to go. You may get lucky in that it takes them some adjustment to hit off the slower pitching but it wont take them long and then it will be on. Another thing to remember is that some of these girls will look like they drove themselves to the game. Your 9 & 10yo players will be against girls that are already 13 or about to turn 13 and as you may know, there is a huge difference in size and strength. I think going from 10u to 12U is probably one of the hardest transitions for pitchers but if you are playing C teams, hopefully it won't be too painful.