The oath in child's speech becomes a secondary character. The basis of the article conprices set expressions, functioning in an informal communication. Most of them appeared in the Soviet period, due to the specific role of ritual in the USSR and the characteristics of the Soviet system of the speech genres. The most significant differences between children's oath are: its formal organization (a narrower repertoire of specific components acting as a guarantee in the case of their verbalization, the possibility of rhyme, stability).