The paper focuses on theoretical concepts proposed by Professor Jerzy Cieślikowski (1916–1977), one of the most renowned Polish figures in the field of children’s literature studies. After providing a short outline of the theories of children’s literature in Poland (with the focus on two scholarly orientations towards the subject of research: ‘universalism’ and ‘autonomism’), the author of the article presents Cieślikowski’s main ideas. The first one, introduced in a monograph on children’s folklore and literature, Wielka zabawa (The Great Play, 1967), claims that such writing is inextricably associated with play, while the second one, which can be derived from essays included in the collection Literatura osobna (Separate literature, 1985), indicates that children’s texts constitute a separate literary system (the ‘fourth’ one, alongside ‘highbrow’ literature, folk literature, and ‘pulp’ literature). As both theories were met with polemics, Polish scholarly debate about Cieślikowski’s concepts is discussed in the paper as well. Finally, the author of the article presents several examples of using or referring to Cieślikowski’s ideas by contemporary Polish scholars, which, in a way, show his continuous impact on children’s literature studies in Poland. Therefore, Cieślikowski’s prominence in the country’s academic discourse about children’s texts, although his theories remain controversial, is indisputable.