This paper presents an investigation into the origin(historicity) of childlike innocence, which was found in the theory on child's heart by Li-Zhi. In Korean literature of children's poetry, it was examined with a focus on the childlike innocence theory by Lee Won-su since no other poets arranged the issues of children's poetry and childlike innocence as strictly as him. Children's poems commonly represent "poems written in childlike innocence," and "childlike innocence" usually refers to "children's innocent and naive mind." "Childlike innocence" is thus a very important concept in children's poems. Both the concepts, children's poetry and childlike innocence, are something "obvious" to everyone. When someone asks what children's poetry and childlike innocence are, he or she assumes both the concepts in mind before asking the question, and the replier is ready to answer the question based on the same assumption. The "origins" of children's poetry and childlike innocence are no longer important. Once a concept is established and acquires "universality," its origin soon disappears. As far as early writers of children's literature were concerned, "childlike innocence" was "children's mind" and "feelings of children that were actually living a life" very obviously. Their mind was clear, nice, and conscientious. Children were supposed to be cheerful and adorable, play cute tricks, and act nice all the time. With no stains on them yet, they were supposed to know nothing about worldly affairs or should not know. When some children said there was something wrong with the world, they would not be children with childlike innocence. As long as such children appeared, the concerned works would become "disturbing literature" rather than "literature of childlike innocence." That idea was so solid and firm that it became a "specter." They saw the world and looked at the lives of children with that idea of childlike innocence. Childlike innocence was an issue of adults rather than that of children from the start both in the old days and early modern times. It is neither the matter of ethics nor that of morality. Ethics and morality already came from loyalty and intellect. They were not something educational or "children's mind." It is strange enough, however, that people always see childlike innocence as a matter of "mind and life of real children." Those who were in proletarian children's literature pressed those who were oriented toward childlike innocence to look at the reality of children right in the colonized country, but the protagonists created by them were children with a beard. It was the overturning of childlike innocence. Those who were oriented toward childlike innocence criticized their works, saying they were not "literature of childlike innocence" and arguing that children should always be free of stains and innocent when they met the main characters solving real issues. It was also the overturning of childlike innocence. Li-Zhi did not call childlike innocence "children's mind." It was merely figure of speech. He maintained that childlike innocence was a true mind, true intention, or the first image of mind. The problem was that when people read his works, they assumed that he defined childlike innocence as "children's mind." It was also the overturning of childlike innocence. Something obvious is always strong. Children are neither innocent nor naive today as well as in the period when he lived.