SF is a great place for kids of all ages. But housing is indeed very expensive, as is childcare. Families in rent-controlled apartments who want more space without significantly higher expense don’t have a lot of options; several such families we know ended up moving out of the city (sometimes to elsewhere in Northern CA but often across the country to be closer to family). I don’t know anyone who moved because they thought their kids were having a bad time in the city.

Yes, but surely those people are not moving to the South Bay (which is just as expensive).