Reading is one of the basic assumptions of the cultural competence of humanity. Children's literature therefore plays an important role in shaping an individual. It is Ivan Kušan (1933 – 2012) who is considered the originator of the modern and contemporary children's novel in Croatia. Children's novels are full of idioms that make the text more interesting and closer to the younger reader, therefore the topic of this work is precisely idioms. The study of idioms is a younger linguistic discipline, which makes it interesting for research. Idioms are an integral part of everyday life, but also of written texts that they enrich. The subject of this paper are the idioms confirmed in the novels Koko i duhovi and Lažeš, Melita by Ivan Kušan, which are certified in two phraseological dictionaries Hrvatski frazeološki rječnik (2014) i Baza frazema hrvatskoga jezika. For all confirmed idioms, the context and meaning is given, but in addition to the above, a detailed classification is also shown with regard to thematic areas. The paper also provides an overview of the structural analysis of idioms.