We did it! My 5 year old son rode his bicycle (no training wheels) all the way around Burke Lake last week. We did have a fairly significant snack break halfway through, but he did it. Mud puddles, roots, dirt, gravel and all. I was sweaty at the end, though it was a warm and humid day. The most impressive sight was certainly the uphills where I pushed the stroller with my left hand and pushed the bicyclist (Tour de France style) with my right. Downhills were super fast, but overall it was slow. If only I wasn't in such good shape ;)
The experience reminded me and perhaps helped me to appreciate that these tiny bodies are much better suited for short bursts - i.e. intervals. Try to pace a 3-year-old. Go ahead. Good luck with that... They run and run and then they crash (hopefully not literally). Why not take advantage of this? I've always avoided "speed word" as it was so much easier just to slog through it at a more even pace with the stroller, but here's a great chance to do a little sprinting.
We'll give it another go next week. For now, we need to get his older sister up to speed so she can come along too. Perhaps we can make a game of it. Sprinting, resting, racing mom, etc. We'll have to do something...it is just the beginning of a long summer.