It is the 2020 Lunar New Year holiday, and 11-year-old Xiaoxiao and her little brother are at home with their grandparents in a remote part of central China. They are anxiously waiting for the Spring Festival reunion dinner when their parents return from their jobs in southern Guangdong province. Like hundreds of millions of rural migrant workers in China, Chen and Liu travel home only once a year. The travel rush over the holiday period, which lasts up to 40 days, is considered the largest annual human migration in the world.