I grew up in Toronto. The Royal Ontario Museum is worth a visit, as is the Ontario Gallery of Art. Just outside of town, the Group of Seven McMichael Gallery in Kleinburg is excellent (if you're into that sort of thing, although your teens may not).
Who knows, with any luck this June the Leafs may still be playing! That would be a pricey ticket but Justin Bieber would definitely be there! (I'm thinking of the teens).
The Jays have a very exciting team this year
Kensington Market is fun and downscale, the immigrant side of Toronto is on full display; the St Lawrence Market is more upscale. Try a peameal bacon sandwich at the latter.
The toronto Islands are relaxing. Rent a bike, a rowboat. If you venture to Hanlan's point, know that there's a nude beach. Centre Island has the carnival rides etc... its kitschy but fun. The ferry ride alone is worth it on a sunny day.
The zoo is vast, I havent been in a while, so i can't comment.
Great walks in the ravines of the Don River.
Lots of plays and musicals in the theatre section (King and Bathurst area) should be on now that covid protocols are eased. Not sure if Stratford Shakespeare festival will be going at that time of year... There's a Shaw festival in Niagara-on-the-Lake that may be running.
Go look at mansions on the Bridlepath (Drake,,, your teens will know who he is). Or more to my taste, the houses in Rosedale.