I think it is way too early to call a trend. And to the degree cities are growing just barely faster than suburbs (.2%) for the last couple years, that can largely be explained by the housing bubble and recession. While there is some data showing young people moving to cities, there isn't much showing families returning to cities.
According to his analysis of the 51 metropolitan areas with more than 1 million people, the primary cities in those metros grew an average of 1.1 percent, compared with 0.9 percent growth in the suburban areas of those metros between July 2010 and July 2011.*
http://www.theatlanticcities.com/neighborhoods/2012/06/urban...