While the camera is useful as something to hold, in order to get the shots you want, you will want to be more concerned with lenses than the camera body.
When you are talking about speed of the lens, you could mean the focus speed or how much light is being let in.
Most people who are new to SLRs, or photography in general, refer to speed as focus speed. After you have learned more about photography, people generally refer to speed as how much light is being let in. The more light that is let into the lens, the lower the number to the right of the f/ mark is. Also, the more blurred the background can get. Though speed can also refer to a camera's speed as continuous shooting mode rated at Xfps; where Xfps means X frames per second. So if this read 3fps, you will be able to take 3 pictures per second at it's fastest setting.
If you are taking pictures of fast moving kids, and are leaning towards a Canon system, I would recommend getting a lens with USM. USM means that the focus speed will be quieter and, generally, quicker than lenses without USM.
One of the best general purpose, beginner, lenses on the market right now is the EF-S 15-85mm f/3.5-5.6 IS USM
Though if that stretches your budget a little too much, you might be able to find a good deal on a used Canon EF-S 17-85mm f4-5.6 IS USM
While the default kit EF-S 18-55mm f/3.5-5.6 IS II lens can get you some good pictures, it doesn't focus as fast as the ones I mentioned earlier. If your subjects are still, this would not matter as much. That said, getting this lens with your camera might be more advantageous if you wanted to just learn more about photography before you go out and get a different lens in the future.