Got my wife to walk to the store with me this weekend. She is very un-confident on a bike and not appreciating my attempts to "help" on that front, so I put the third wheel jogging attachment on the bike trailer, tossed in the kid, and off we went. It is a 1.8 mile walk to the store, and it rained on the way back, but I thoroughly enjoyed it. My wife didn't even leave me afterwards! I wish there was a better route, as the direct path is on a major street with lots of road noise.
At 4 years of age our kid enjoys activity, but can't handle near enough for us to get enough exercise playing along with him, and often we just end up with back pain from working down at his level. So we have to resort to things like this, or in my case biking 9 miles each way to the zoo so he can run around there for his exercise.