What lenses with Canon 40D -main interest kids sports, nature ?

The 70-200mm f/4L Would be perfect for Sports. The 28-135mm lens doesn't have the Zoom ability, or the Superior L quality as the 70-200mm f/4L- Getting it without IS would be fine too- but if you have the money spend it. Note: the 70-200mm lens is very heavy, and you might need to mount it on a tripod to use it, it's no small lens. The 28-125mm lens is much smaller, for the hand-held sort of photography. I suggest the 70-200mm lens, but something So heavy can even create more camera shake even with the IS, so you can get a tripod too, they aren't that expensive. You'll enjoy your L Lens.