Photographer documents plight of China's left-behind children

For more than three years, photographer Ren Shichen has traveled across China taking portraits of the country's left-behind kids -- some of the estimated nine million young kids are currently growing up without Mom or Dad in China.
His goal is to shed light on the psychological costs of China's economic boom -- the ones borne by rural children whose parents have left their villages to work in China's cities, often for years at a time, leaving them in the care of grandparents or other relatives.