Fig. 1

Stratified sample units of kindergartens of different levels in Hainan. There are 4 prefecture-level cities, 5 county-level cities, and 10 counties/autonomous counties in the Hainan administrative division. Among the 4 prefecture-level cities, there are 4 municipal districts each in Haikou and Sanya Cities. Danzhou City is taken as a county-level city, as it governs only streets and towns. We deleted Sansha City due to underpopulation. Thus, there is a total of 3 groups and 24 categories of primary sampling units, including 8 municipal districts, 6 county-level cities, and 10 counties/autonomous counties