Children’s art activity is a way to draw out their internal world, expressing their experiences creatively. In the development of children’s paintings, every stage has its own characteristics, as in the physical growth and mental development of human beings. This study is to provide basic information on how to better understand and teach children in painting by employing the following methods; analyzing children’s paintings with synchronism, one of the characteristics that often appear in the composition of the paintings; examining the contents of synchronism as are shown in this analysis; considering how synchronism varies with children’s ages and sexuality and the themes of the paintings; defining the characteristics of paintings. For this study, for seven months from March 1986 to September 1986, 1,600 paintings have been collected from 1,823 children aged from five to twelve attending kindergartens and elementary schools in Seoul. Each child was asked to paint a picture from two given themes. The paintings have been grouped into those of common expression, synchronic ones and the others somewhere the above two groups, and then examined in terms of synchronism according to ages, sexuality, and themes and dealt in percentage in statistics. This study reveals the following: First, synchronism is a temporary phenomenon that is outstanding with those at the ages of six and seven, but not with those over the age of seven. Second it is more detectable with girls but chiefly at the similar rate with both sexes at the same period. Third, it is distinct in the paintings with particular composition such as those from “Mealtime or Birthday.” The study also shows to the paintings with synchronism have proved to be of rich contents with strong characteristics and to be well composed without being slant to one direction. It is revealed that this phenomenon of synchronism, one characteristic of expression conception, is closely related to the development of recognition. Synchronism is also a phenomenon which gradually decreases in its appearance with children after the age of seven. I wish that this study can help understand children in terms of the development of their paintings as well as the physical growth and mental development and at the same time will be useful for children’s education of fine arts.