The research focuses on the issue of mixed-aged children in nursery schools. The aim of the research was to find out the opinions of the nursery school teachers on the advantages and disadvantages of a heterogeneous age groups based on their practical experiences. In order to find out the opinions of the respondents, a questionnaire was constructed and used. Based on the results, it can be said that 243 respondents consider an advantage to be the better social and emotional development of children, regardless of whether the respondent prefers to work in a homogeneous or heterogeneous age group. However, they did not agree with the disadvantages of heterogeneous age groups. The respondents teaching homogeneous age groups have generally identified far more disadvantages, and the greatest disadvantage being that children in a heterogeneous age group have worse conditions for cognitive development and do not have the opportunity to compete with each other. It has also been confirmed that those respondents with more years of work experience prefer a more heterogeneous age composition of groups than respondents with fewer years of work experience.