I love hiking. When the girls were too small to walk it was easy to put them in a jogger. I chose wide open trails. But next came a phase when they can walk but not as long or far as I wished. Neither one of us gets a work out really. I don't want to be mean mommy but since when does a 3 year old have less energy than me? I found a trick that has worked with both of my girls.
For my oldest, I would say "There's pirates in this land and they dropped their treasure on their way to higher treasure!" She would come running....and keep running to find the next treasure! For my youngest I say "The pirate princess came by here and she left you a trail to find her!" It's amazing how well it works!
How well does it work you ask! I've done 2 hour, straight up the mountain kind of hikes in Big Sur on our way to waterfalls. And last week we did a 3 hour hike in Griffith Park to find the Japanese Teahouse! I didn't pick up the 3 year old once and the 7 year old wishes she could run the trails by now. I have a bad back so it's kind of a necessity for me to have them walk on their own.
Of course I make sure you keep the kids well hydrated and fed! Snacks are the other thing I keep well stocked in a backpack! Both girls have built up quite a bit of stamina over the years/months. My oldest can now do my usual hikes. Except, she prefers to run them and so I'm the one struggling to keep up with her.