I tried to start my kids out pretty young but they still like to complain, the exception now is my 10 year old can crank out some miles and enjoy it. We'll see what the younger ones do over the next few years. I just started a kids album if you want to add this pic to it. (kids of summitpost)
I think ot is good idia to open such an album you can use my images. By the way I just launched the album " Start hiking with preschoolers"