For more than a three years, photographer Ren Shichen has traveled around China taking portraits of the country's left-behind children.

Each child poses in a classroom with a message for their absent parents on the blackboard behind them. Here, Gou Lingyu, 6, from Gaomiao Elementary School, Balipu County asks: "Mommy, where did you go? Mommy left home when I was six months old. Daddy cooks for me every day and works in the field and takes me to school. On the left hand side of the board is written: "Mommy, are you coming back?"

Ren Shichen

Wang Zixuan, 8, Gaomiao Elementary School, Gansu: "I miss daddy and mommy. Daddy and mommy went out to work. I haven't seen them in three years." Ren Shichen

Zhao Jinbao, 7, Matan Elementary School, Gansu. His message reads: "Dad, when are you coming back? My dad went to Baiyin to work for a year. Mom cooks and works in the field."

Ren Shichen

Zang Yixuan, 5, and his brother Zang Yaxuan, 4, at Ma Tan elementary school. Their messages read: "Mommy wants to have another boy." "My mommy wants to give me a little brother." Ren Shichen

Wang Baohua, 11, Majiawan Elementary School, Longmen County, Gansu. "My dad comes to join my mom's family. I like daddy. He always buys me good stuff. Daddy and mommy love each other. Grandpa and grandma also like dad. Happy family."

Ren Shichen

Ma Haishan, Bulengou elementary school, Gansu. "I want to be a doctor when I grow up. My dad passed away because of stomach issue in May, 2012. I miss dad very much. I want to be a doctor to treat more people in the future." Ren Shichen

Ma Jincai, 7, Bulenggou Elementary School, Gansu. "I want to be a policeman. My dad was buried in 2011 when he was digging coal."

Ren Shichen