Statistically speaking, wealthy people tend to have fewer children, and have those children later in life. I believe this was true for the previous generation, too.
>the 1 BR in SOMA isn't going to cut it at that point and there will be a flight back to the suburbs.
Yeah, but a 2 BR would work just fine, especially if you only have one kid. And 3 BR apartments are not unheard of. (and the cultural changes required to expect kids to share a bedroom are not impossible.)
I think that the deciding factor here is perceived safety, followed by quality of schools. As cities are gentrifying, people seem to be thinking of them as safer. And a wealthy population (especially a wealthy population that recently moved in, and here in California, is therefore paying full freight property taxes) makes for a bunch of money to throw at those problems.
If cities start being perceived as safer than suburbia? That could push parents out of suburbia and into cities. That's how they got to suburbia in the first place, right? And it's a self-reinforcing cycle; gentrification means more taxes, more resources for law-enforcement, (and conversely, less of those things in the suburbs, if the wealthy folks in the suburbs are moving into the cities.)