Interpersonal interactions during childhood form the foundation for development and learning (Tomasello, 2014; Vygotsky, 1962, 1978). Numerous studies have documented the impact of interactions between preschool teachers and preschool-aged children between 3 and 6 years of age (e.g., Denham et al., 2003; Hamre, Hatfield, Pianta & Jamil, 2013). The aims of this 1-year observational study were to investigate patterns of interaction between professional preschool teachers and children between 10 and 24 months of age in Danish crèches and to examine the correlations between these interaction patterns and preschool teachers' pedagogical decisions. The study indicates that internal pedagogical choices (extent of reflection and planning for the pedagogical activities; criteria for groupings of children; whether preschool teachers worked predominantly alone with smaller groups of children or as a team of two or three with several children)--decisions that differ from crèche to crèche--are crucial. These pedagogical decisions are mutually dependent on or sensitive to the child-adult ratio. The study reveals significant differences in the character of the interpersonal interactions between teachers and children, according, for example, to the level of planning and pedagogical reflections. This may cause different conditions for children's cultural learning and development.