Brooke91, enjoy the nice weather. In Ontario we are used to the heat and humidity and yeah the smog alerts that come with it.
Just make sure that while you are outdoors the kiddies have water available to them at all times. Sunscreen and of course hats, but if we are in the shade, I allow the kids to take off their hats as many of the kids sweat horribly in their hats.
I do water table and sprinkler. I do have a hard kiddie pool. My husband made a plywood cover for it so it is covered when not in use and no child can remove it.
If there is a heat alert and or smog alert, we will go out first thing in the am and that maybe it for the rest of the day. Enjoy! (Heard Edmonton reached a humidex of 40C today!!)