I am happy that Mississauga has its own downtown core where everyone can enjoy all sorts of events and concerts in an open area. I've never been to their outside movie or exercise programs but I'm sure many families are outdoors enjoying the free open space.
The events I'm always here for are Ribfest, Canada Day (if I'm in town), or most outdoor events that involve food (i.e. Japanese Festival, SoundBites). I am huge food truck fan so if Celebration Square announces that a swarm of food trucks are in town, you can bet I will be there.
For bigger stuff, Celebration Square may not be big enough to hold everyone. With Canada Day, you would have to bring your own chairs and stay in that space until the fireworks explode in the air or find a seat alongside a concrete curb and end up sitting there for over an hour (your butt will hurt big time). Unless your okay with standing on your feet and walking around then be prepared to squat in one place.
Best part is, most events are free and it is a wonderful experience to get out of your house and enjoy the entertainment with family and friends.