please help: lens for the Canon XTi

Hi! I have decided on the Canon XTi camera, but heard the lens coming with the camera is not good. So I am looking for a separate lens. I would use the camera mostly for indoors kids portraits/performance and outdoors kids soccer games. Is there ONE lens that can fit all my needs? I got recommendations of canon 17-85 and canon 70-200/f4L from the camera shop, but not sure if they are good ones (and I really don't like to carry two of them with me). Thanks in advance for your suggestions!