Right down near the Air Canada Center (where the leafs play) is the CN Tower. There are some cool things going on there usually. They probably have a website if you google it. You can't miss it, it'll be the HUGE tower in the middle of the street.
Other than that, there is the Ontario Science Center, which was pretty cool when I was growing up. There is also the Royal Ontario Museum, which has dinosaurs and stuff. Plus there is the Toronto Zoo.
CN Tower will definitely be the closest. You might want to get the address for the Air Canada Center and then do like Google Maps to and from any of the other locations, because I know that the Zoo, for instance, is probably going to be an hour away from the arena.
Avoid Young street after dark. There's not a lot of trouble there, but there is a red light district and a few nefarious sites I wouldn’t want a 9 year old seeing. [img]/images/graemlins/wink.gif[/img]
As mentioned above, the Science Museum is a must for a 9 year old!