SICHUAN , China ( CNN ) -- Li Yunxia wipes away tears as rescue crews dig through the ruins of a kindergarten class that has buried her only child -- a 5-year-old boy . Other parents wail as soldiers in blue masks trudge through the mud , hauling bodies from the rubble on stretchers . `` Children were screaming , but I could n't hear my son 's voice , '' she says , sobbing . This grim ritual repeated itself Thursday across southwestern China , as thousands of mothers and fathers await news about their sons and daughters . Watch parents ' anguished vigil » . The death toll from Monday 's massive earthquake could be as high as 50,000 , according to state-run media . Map » . The grief is compounded in many cases by a Chinese policy that limits most couples to one child , a measure meant to control explosive population growth . As a result of the one-child policy , the quake -- already responsible for at least 15,000 deaths -- is producing another tragic aftershock : . Not only must thousands of parents suddenly cope with the loss of a child , but many must cope with the loss of their only child . China 's population minister recently praised the one-child rule , which dates to 1979 , saying it has prevented 400 million children from being born . Some wealthy families ignore the order , have more children and pay a $ 1,000 fine . In rural areas -- like earthquake-devastated Sichuan province -- families can petition for an additional child , but there 's no guarantee the authorities will approve the request -- they usually do n't . That reality has cast parents like Li into an agonizing limbo -- waiting to discover whether their only child is alive or dead . Thousands of children were in class when the temblor hit Monday afternoon . Many of their schools collapsed on top of them . In Dujiangyan City , more than 300 students were feared dead when Juyuan Middle School collapsed with 900 students inside . A similar number died at the city 's Xiang ' e Middle School . See images and video from the quake zone » . Now parents cluster outside collapsed school buildings , held back by soldiers in some cases as rescue crews search for signs of life . `` Which grade are you in ? '' a rescuer asks a trapped child in Beichuan County . `` Grade 2 , '' comes the answer . `` Hang on for a while , '' he says . `` We are figuring out ways to rescue you . '' Watch children rescued from the rubble » . The child is pulled from the rubble a short time later . For every child saved , though , many more are lost . Many are missing at a middle school in the city of Qingchuan . The scene is devastating at Juyuan Middle School , where sorrow seems endless . See photos of rescue efforts » . `` There were screaming parents , and as the bodies would come out they were trying to identify whether it was their child or not , '' said Jamil Anderlini of London 's Financial Times . `` And once they -- the parents -- realized it was their child , obviously they collapsed in grief . ''
NEW : Death toll could reach 50,000 , according to state-run media . Sichuan province 's 50,000 -child policy , implemented in Monday , has blocked 400 million births . Many parents in limbo as they wait to learn whether their sole child is dead or alive . Schools collapsed on 400 million of children 1979 when the quake hit .