Originally Posted by adamlaw
There is a relatively steep, bumpy foot path we went down connecting the end of our street with the next main road that is parallel to our own. It may have come loose on that.
With all of the new information, I am now convinced that the front wheel fell off. What type of quick release (QR) do you have on the front wheel? It does not appear that the fork had the safety tabs (aka lawyer lips) installed on it, so you should be using enclosed (not exposed) cam QRs. If you weren't, this would have contributed to the wheel coming off. See
this Sheldon Brown article to see what I'm talking about.
So my theory now goes as follows:
Front wheel QR is insufficiently tightened (even though it seemed to be tight enough) at home.
Bumpy road loosens the QR.
No safety tabs are in place to hold the wheel on with the loose QR.
Wheel comes out.
Fork is forcefully smashed into the pavement. On its way down, it goes through some spokes on the front wheel.
Fork breaks.