Johnston Canyon was spectacular, and a perfect short hike to take our 5-year-old on. We trekked to the lower and the upper falls, and back, for a total of about 5 kilometers. It wasn't until we reached the last stretch before the car that our son asked us to pick him up and carry him because his feet were getting sore. Considering how far he walked, and the elevation we gained, we didn't mind.
It made us laugh that it was raining at the bottom of the hike, and by the time we reached the upper falls the sun was out and we had dried off -- only to hike back down to the bottom where it was still raining.
There were so many amazing views and things to see in such a small amount of space. Nature is such a wonder. My only disappointment was in was the fact that people couldn't be bothered to hang onto their trash until the could find a bin, throwing it just to the side of the path instead. Johnston Canyon deserves more than that.