Shortly before we moved away from southern Utah we took our kids to Kanarra Falls. If you are ever in the
area in the summer, I highly recommend it. It was 25 degrees cooler than St. George, and in late July it felt absolutely heavenly. My kids still talk about this hike on a regular basis and it was my favorite family activity that we did this summer.
To get to Kanarravile you take exit 41 off I-15. Travel north until you hit the tiny town (the highway turns into main street) and turn towards the mountains (East) at 100 North. There is a parking lot at the base of the trail. Parking is $10, they only accept cash, exact change. (But there is no further charge, this is not part of any national or state parks.) If the lot is full, you can park further into town at designated places, but it will make your walk longer. The hike winds in and out of the river, and through a slot canyon, with 2 waterfalls to climb over. There is also a natural rock water slide that spills into a small pool, but my kids were afraid to try it. It can be as easy or as hard as you make it. Round trip to the first waterfall is 3.5 miles, 3.7 miles to the second, and 4.4 miles to the end. You can turn back at any time. We did four miles with our little family of five (including toddler) and it took us about five hours (that includes stops for lunch and snacks). But we went at a very leisurely pace, looking at flowers and wildlife.