We went to Calgary last summer with our kids (1 and 3) with the majority of our time spent doing dinosaur related things for my son.
Drumheller was definitely a hit! My son (3) LOVED the museum, especially matching the dinosaurs to the maps. Since you said you've been there, you may already know about the dinosaur statues around the actual town, as well as the little splash park. The kids loved walking to see the statues!
In Calgary, we did the zoo and a couple little splash parks. I don't remember exactly which ones we went to, but from what ours friends in Calgary have said, all of them are good, so maybe there's one close to where you will be.
As a kid, I remember going to Calaway Park and had so much fun. We didn't have time to go when we were there so I don't have recent experience, but I'm sure it's still great!
We ended up going to Edmonton as well (not sure if that's realistic for you), but north of Edmonton there's a big dinosaur exhibit similar, but bigger, than the one in Winnipeg Zoo called Jurassic Forest. We went that far north just for it and it was definitely worth it for our family. My son still talks about it!
Have an awesome trip! I'm sure the kids will love it!