Many Chinese kids, known as "left-behind" children, hardly ever see their parents, because their parents are migrant workers. Li Ling, 11, is a left-behind child. Her parents have been working in Zhejiang for 10 years, while she lives with her grandparents in Guangdong. She was reunited with her parents last Spring Festival. As the number of migrant workers in China increases, the number of left-behind children is rising fast. Li is one of the 61. 02 million left-behind children under 17. They account for 37. 7 percent of rural children and 21. 88 percent of all Chinese children The large number of left-behind children has already become a social issue. If left unsolved, it will cause serious problems, Wang Zhenyao, director of the China Philanthropy Research Institute, told China Daily. The education level of adults supervising  these children is generally not that high. They can only take care of the children's personal safety and daily living, being unable to care for their educational and spiritual needs. Meanwhile, the absence of parental support will make some left-behind children lack self-confidence. They may be slower in physical and emotional growth than their peers. Others may even become "problem youths". To solve this problem, the government is taking action. For instance, 30 provinces and cities have allowed certain children to attend school and take the college entrance exam in the city where their parents are. However, Wang suggested that the country do more, such as making policies encouraging migrant workers to work in their hometowns. He also said that a well-balanced child welfare system is needed. "These children are the future of the nation, so they deserve our loving care and protection," Wang said. The purpose of the passage is   _  .
to criticize the migrant workers who leave their children at home to focus on the present situation of the left-behind children to worry about the present situation of left-behind children to call on the government to educate the migrant workers