In Sweden, preschool has been noted as being of a high quality compared to many other countries. However, dramatic changes in the preschool sector are taking place. A recent law states that it is a child's right to get a preschool place within a few months. As a consequence, the number of children in preschool has increased, which could influence group sizes since there is no state regulation of the number of children in a group. This article based on the project The impact of group size on children's affordances in preschool aims to describe and analyse preschool teachers' ideas of what an ideal preschool group is. It is a qualitative study based on a questionnaire with mainly open-ended questions, answered by preschool teachers. The results show that preschool teachers define a well-functioning group as having a balance between gender, age and ethnicity. The preschool teachers stress that they prefer a group with fewer children than they have today. A key aspect of having a well-functioning group is also the preschool teachers' competence and the preschool environment. Preschool teachers' ideas of what constitute an ideal group of children may contribute to why they perceive the group size too large. (author abstract)