With the deepening reform of economic system and the acceleration of urbanization in China, a large group of left-behind children who are showing new characteristics in social changes have begun to emerge. This study aims to explore the cumulative disadvantage pathways and coping strategies of left-behind children during their developmental stages within China’s unique socioeconomic context. This study employs semi-structured interviews and participatory observations to obtain interview data from a total of more than 500 left-behind children and related subjects across 10 districts and counties in Chongqing, a large population exporting province in southwestern China, including Dazu, Youyang, and Pengshui. Then it utilizes the interview records as data for qualitative analysis to summarize the developmental disadvantages of left-behind children at different ages. The study has believed that the number of left-behind children in China is huge, mainly clustered in western China, which has given rise to new situations such as diverse types, complex problems, frequent transitions between staying behind and mobility, and career development difficulties. After analyzing different age groups in a similar way, this study has revealed the accumulation of disadvantages in the developmental stages of the left-behind children: (1) during infancy, the parents’ helpless decision to “go out” and their lack of sense of responsibility result in the absence of family education for the left-behind children; (2) during the preschool years, the development of early speech and behavior ability of left-behind children is affected by the guardians’ laissez-faire parenting and bad habits; (3) during the school years, the broken home-school connection, insufficient supervision and encouragement and poor academic performance intensify the children’s inferiority complex; and (4) during adolescence, under the influence of the social environment and the long-term accumulation of disadvantages, the left-behind children’s role perception becomes confused, and then they fall into a crisis of self-identity. It can be seen that the cumulative disadvantages of left-behind children are the result of multiple factors, which is difficult to be stopped just with a single force. In view of the cumulative disadvantages of left-behind children in China at different stages, this study has made the following proposals: (1) family support capital should be enriched, and parents’ sense of responsibility should be strengthened; (2) guardians and communities should form a joint force to raise children together; (3) the school security system and the collaboration among multiple stakeholders should be promoted; and (4) a socially friendly atmosphere should be created, and active preventive measures and guidance measures should be taken.