About 80% of folks I know with kids leave San Francisco before they turn 5. The big issues are high rent, variability of school quality and logistics getting kids+gear around. City has done some great work to upgrade the kid's parks but the rent, schools and logistics make it very expensive to raise kids in SF.

It depends if you mean SF or are including the surrounding area.

The few people I know with kids in SF proper are either dual-income or did well on a startup. Some people live in the Sunset, which is more suburban -- still expensive but at least a little more kid friendly.

Most everyone else I know leaves the city for a suburb. Essentially having kids means your commute gets longer!

(Although in my case it actually got a lot shorter because I also got a job a lot closer to home in the South Bay instead of working in SF).

Dual income. Very little left over.