Let me offer the perspective of a not so young, not so childless resident of the not so sunny eastern US: dense, walkable cities are awesome for people with young children.

Weekends in the city with our toddler are awesome. We have brunch at one of the dozen restaurants we can get to within a few blocks' walk. We can walk to the park, walk to the drugstore to get the diaper cream we forgot to buy. We can have impromptu, unscheduled social events just by running in to the 3-4 other couples with kids our age who live in our apartment building. And narrow little pedestrian-oriented streets, which we don't have where we live but would love to, are a whole lot more toddler friendly than ones primarily designed for cars.

If anything, the advantages of city living are magnified for people with kids. When I was single, I thought nothing of driving 15-20 minutes on a weeknight to meet some friends for dinner. That's a non-starter with kids. These days, 70-80% of our social interaction is hanging out with people from our building.