The website Toronto for Kids has a GTA-centric list of free events which I think has a lot of good ideas...they include how to get free entry to museums, etc...
The best things to do for families this summer (in the GTA) which are 100% FREE!
http://www.toronto4kids.com/June-2016/100-Free-Things-to-do-this-Summer/
Pack tons of patience, hats, paper and pens (ultimate entertainment systems) and snacks and footwear suitable for sidewalk pounding. I don't know how kids don't say their feet are sore from walking in flipflops for hours (or stubbing toes into planters, metal posts, etc.) in urban spaces.
As part of Harbourfront's Canada Day celebrations, there will be a Montreal francophone hip hop act performing before the fireworks display. Good way to keep one's French in active use is by attending cultural events!
http://l-express.ca/du-hip-hop-montr...ada-a-toronto/