Leto has pretty much pegged the touristy bits / things to do with the kids.
There is also Canada's Wonderland about 45 minutes north of downtown if you are into amusement parks.
http://www3.paramountparks.com/canad...rland/#actions
The thing that makes Toronto great is its neighbourhoods though (I don't know how much your kids will care though, and pretty much anywhere you go, they have to go.
Queen Street West
College Street (little Italy (so called, though to me, it's Dufferin and St. Claire)) around College and Bathurst westwards
Yonge Street (Main drag)
Bloor Street from Yonge Street westwards.
Queen Street East - Beaches (one of my personal fav's as Leto mentioned. The boardwalk, the shops on Queen.)
Oh, and there's the Royal Ontario Museum (ROM) located on University and Bloor. That'd be a cool place for the kiddies.
http://www.rom.on.ca/
There's the Art Gallery as well.
http://www.ago.net/navigation/flash/frameset.cfm
If you are into nature, there' s High Park, which is Toronto's Central Park, only it's not so central, more west end. But there's Shakespeare in the Park and a small zoo, nature trails, etc.
http://www.toronto.ca/parks/highpark.htm
Then there's the general webpage
www.toronto.ca
or the info page
www.toronto.com
Then there's the Harbour boat cruises - night time is cool. Very touristy, but the view is pretty cool.
Oh yeah, it's Torontonian.
And please, whatever you do, please say the name of the City correctly.
Terranah.
Americans can always be caught saying TOE RON TOE
It's like finger nails on a chalk board.