If you have time, I'd suggest taking your kids to the Royal Ontario Museum, then walking through the nearby University of Toronto grounds (which you will recognize from a lot of movies). A Blue Jays game is always a good time, and the area around the stadium has a lot of good restaurants.
The best part about Toronto is that it is incredibly safe. You could let your kids ride the subways on their own or walk around downtown if mom and dad ever want to take a break.
It's been a while since I went to it but there is also the Ontario Science Centre.
The kids might enjoy the Famous People Players. It is a supper theatre with a black light show in which all the performers are developmentally challenged teens. The professionalism of the productions is amazing.
Are the teens interested in legitimate theatre or concerts? If so, there are legitimate theatres, concert halls and open air concerts.
If you come to Toronto between August 15 and September 1 the Canadian National Exhibition will be open, This has several buildings full of displays and a midway with rides and sideshows. There is also an air show.
About an hour's drive west of Toronto is the town of Stratford which puts on the Stratford Shakespeare Festival every summer. It features Shakespeare's plays but also more modern productions including musicals.