My wife and I have no children nor immediate plans for any, but we live just a little over two miles from my job. Hers is a bit further, but still only about four miles. That means that, if I take it very, very easy, I can get from door to door in about 15 minutes. If I only take it pretty easy, it's more like ten minutes or less, depending upon how I hit the traffic lights.

For me personally, my commute isn't an opportunity for recreation, it's just getting to work and back. I get plenty of riding in when I'm not commuting, so I don't need to add miles there. The big benefit I get from such a short commute is flexibility. It is always possible to add riding time if you want to do that, whether by taking a long route home or by riding more at other times. It isn't really possible, though, to subtract time from your commute when you want to do that. If I find that flexibility valuable with my relatively low-commitment lifestyle, I can only imagine how valuable it would be if I had a child on the way or already in the house.