I agree with FigmentSpark: you'll probably have a better chance at finding local advice on the Canadian board.
I can't give specific advice for Vancouver, but in general terms, if you have small kids you might want to consider checking out some of the suburban celebrations rather than the main Canada Place venue. We live on the outskirts of Ottawa; as the capital it is always very busy downtown on Canada Day with various headline performances and big crowds. We used to enjoy going downtown as young adults, but when our kids were small we preferred our local suburban celebration where there were still fun things to do (live music, variety acts, and bouncy castles for the kids), but in a more contained area and smaller crowds. If you are staying downtown it might be more time consuming to get out to the suburban areas, but I'm sure there are public transit options.
This site lists some of the options beyond just the main downtown venues.
North Vancouver looks like maybe one of the better choices for younger children, if you care to make the effort to get there.
Hopefully you can get some input from a local Vancouverite!