I would recommend the ferris wheel, mini golf and the indoor water park. Other than walking up and down Cliffton Hills I wouldn't visit any of the attractions. Some like the view from the tower but I've never been there. There is a butterfly sanctuary just before crossing the border into the US that is quite nice.
You are also not far (maybe a 30 minute drive) from Niagara-on-the-Lake which has amazing bike trails along the Niagara River. The parks are gorgeous and many people pack picnics and eat lunch on the grass. The Niagara region is also a renowned wine area, so doing a bike tour of the wineries is an idea (not sure if that's something you would enjoy with the kids though). The town of Niagara-on-the-Lake is very picturesque and quaint with lots of little shops and restaurants.
Personally I'd rather bike in Niagara-on-the-Lake or see a show there (they have great live theater) than spend a day visiting the tourist traps at the falls. Just my $0.02.