They are pretty big for great wolf lodge imo. They may enjoy it though. It is the opposite of cheap. More than $500 a day by the time you get done. I wasn't impressed at the amount of broken stuff for that price. There is another hotel waterpark that is cheaper at Fallsview.There is some grey wolf lodge near Niagara, which seems popular for family's with kids, indoor water park, I think there is a outdoor tree climbing thing near there as well.
If you want to cross the boarder Six Flags Darien lake might be of interest
Wonderland, Blue mountain, The Zoo, Ripley's Aquarium, Niagara Falls
Usually mini amusement parks will start popping up in the weeks leading up to The Ex (at least in To)