Though they're too young to understand what they did for Philadelphia, we can thank babies for the city's eighth consecutive year of population growth. Without the city's births and an influx of residents in Montgomery and Chester Counties, according to updated census figures released last week, Pennsylvania wouldn't have grown at all.

As life-affirming as last year's arrival of 23,145 babies is, they herald a lot of work for the adults who didn't contribute as much to the increase. Philadelphia did not grow because of droves of new businesses - the force that likely fueled the suburban gains. The city has added jobs, but not enough, and its adult population burst seems to be abating. That has demographers worried that the positive trends of the last few years may not be sustainable.

The findings put pressure on the next mayor to craft a credible plan to keep up the momentum.

The raw material is here. A Pew Charitable Trusts survey released last week showed that Philadelphians are more optimistic about the city's future than they have been in at least six years. Two-thirds said they saw better days ahead for the city.

There is plenty to feel good about. Center City continues to prosper, with stylish new housing, restaurants, and shopping. Neighborhoods that were written off are taking off, spurring a spirit of renovation and renewal that is spreading. Parts of North Philly are among the latest potential hot spots.

But the heart of strong neighborhoods is families. Without better public schools, the city won't have enough to offer them. Newcomers attracted by urban vibrancy may decide to move on if the condition of the public schools forces them to compete for limited space in magnet schools or pay for private and parochial schools.

A mayor paying more than lip service to education, with workable plans to improve funding, governance, and performance, has a chance of keeping new parents in the city. That's the least Philadelphia's adults can do for the babies.