You'll be active guiding your kids but you'll be fine.
It is a blast. I recommend life jackets as 2 of my non swimming friends ran into the train bridge. It's clear and visible bridge you just need to get over when you see it.
It's more rafting than tubing. I'd want my kids connected to me just because of that bridge and the physicality it takes to continuously guide your tube out of the bushes.
The portneuf is great. One of my favorites.