You are going to need a lens for that bad boy. I'm not sure what your budget is, but based on the body, here are a few suggestions:
The "kit lens" - This is the lens that is usually packaged with the body, the Ef 18-55. There are a couple of different versions of this lens, the original, which is the non IS (image stabilization) gave this lens a very bad name. It was renown for poor build quality, bad focus, and really bad chromatic adoration (color fringing around high contrast areas). The newer version, the IS version, is quite a bit better, but about 50 bucks more. The IS is not a bad lens for the cost, but still not a stellar lens.
The "Nifty 50" - the ef 50mm f/1.8, about $80. Although this lens is a prime (it doesn't zoom at all) I would recommend it over the kit lens if you can live without a zoom. Still the same build quality (plastic fantastic), but better image quality, and a lot faster than the kit lens, which means this lens will let in a lot more light than the kit lens, so you can take images in darker situations at the same shutter speed.
The EF 50m f/1.4 - About $220 more than the nifty 50, but the advantage is better build quality, and full time manual focus (which neither the nifty 50 or the kit lens have), so you can auto focus on a subject and without flipping a switch on the lens, manual focus to fine tune. It will also autofocus a bit faster than the f/1.8. If you have the cash, this is a fantastic lens on a Rebel body.
The EF 85mm F/1.8 - Very similar both in price and build quality (actually, it is build a bit better than the 50 F/1.4, and even faster focus), but just a little longer, which will help you get closer to your subject. This is a great tight portrait lens, and would probably be good for kids indoor sports.
I would say on the Rebel type sensor (APS-C sensor) the "gold standard" for a nice walk around zoom lens would be the EF-S 17-55 F/2.8. This is an amazing lens, great zoom range, fast, nice build quality, but much more than those listed above. Again, I'm not sure what you budget is, so this might be totally out of the range, but a great lens.
Beyond lenses, you are going to need compact flash cards for the camera. The Rebel doesn't make huge files, so you can probably get by with a pair of 2GB cards ($20 for SanDisk cards). You might want to get a card reader, so you don't have to plug the whole camera into the computer to down load your images.
Beyond that, it is really just accessories. A tripod and a flash are the two big ones that come to mind, but you certainly don't have to pick those up to get started. Unfortunately, photography is a expensive and addictive hobby, so you will always find things to spend money on, but really, the body and the lens is all you really need.