"Why not just manually focus near the center of the stage?"
Exactly! This is the correct way to do it. Unless you are tracking a single dancer. The OP is going to have to rely of DOF if several dancers are the goal. AI-Servo will not work here. Possibly not even AF at all.
And Tim Campbell is off the mark about lenses too. There is no need for a f2.8 lens here either. Unless one dancer is the goal.
The camera set to Av and f8 with the ISO as high as can be accepted will work. Like I said, all cameras have a limit and this may be beyound it.
The OP has the right idea, try it. Trying several different exposure settings will tell the tale.
"I need to find some kids playing to test the different settings on"
Yes, now you are thinking. This will tell you if you can do it. Remeber the larger the f number the greater the DOF will be. Also the higher the ISO number the less quality you will see. You need to find this balance. With the camera set to Av mode, it will select the fastest shutter speed possible.
EB
EOS 1DX and 1D Mk IV and less lenses then before!
