Toronto is AMAZING in the summer, with a street festival happening seemingly every weekend. Taste of Danforth (Greek neighborhood) for example, is running Aug 11-13. The same weekend, there is Taste of Vietnam happening. Chinatown (Spadina and Dundas one) is holding a street festival Aug 19-20.
Salsa on St. Clair is a Latino-themed festival with food, etc. and runs July 8-9. Caribanna is Aug 3-7.
July 7 - 23 is Summerlicious (set prices for lunch and dinner at participating restaurants around the GTA).
Jays games are always fun! $1 hot dogs on Tuesdays and every Sunday is Jr. Jay's Day for the kids, where there are lots of stuff for the kiddies to do at the game, and kids are also allowed to run the bases before the game (no to parents though!).
https://www.mlb.com/bluejays/tickets...r-jays-sundays
Honda Indy is at Exhibition Place from July 14-16. There's also Wonderland you could go with the family which is always fun!
Trinity-Bellwoods park is a very nice park where people go, lay down a blanket and have a picnic, play frisbee, do whatever. Check that out if you and your family would be interested in something like that. It's at Queen and Shaw.
Since you're going up to Markham, if you like Chinese food, tons of solid options up there for Chinese food (it's a city similar to Richmond, BC with a high concentration of Chinese immigrants).