Freezing action requires a fast shutter. A fast shutter doesn't allow ambient light much time to bake an exposure onto the sensor. There is usually not enough light indoors to work with a fast shutter so one of two compensation measures must be employed: 1.) use a wide lens opening (aperture) and/or 2.) boost the ISO sensitivity.
1.). Aperture solution not possible with basic kit lenses. You would like something like an 85mm f/1.8 or a 70-200 f/2.8, which allow over 4 times or over 2 times more light (respectively) into the camera as compared to a kit lens.
2.). A crop sensor camera will look worse at equivalent high ISO than a full frame camera. I don't think you much want to exceed ISO 800 on the Rebels. You would probably get about the same image quality on a FF 6d at 2 stops higher ISO (about 3200).
Between the 2 stops you'd gain with a 1.8 lens and the 2 more stops you'd gain in high ISO image quality on a full frame sensor you could be getting something like 16x more light to work with than what a Rebel and kit lens allow. Divided up between raising shutter speed and lowering the digital noise that is a big difference.
The 85mm or the similar 100mm Canon lenses are only about $325 or $375 on sale. That is a cheap way to make a big difference immediately, and both will also mount on a full frame camera if you switch over some day.
Good luck!
Scott
Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites
Why do so many people say "FER-tographer"? Do they take "fertographs"?
