The transition to formal education is a critical transition in children’s lives that has importance for socio-emotional and behavioral functioning. In the transition process, teachers are key players who work intensively with children and their families. This article focuses on teachers’ perceptions of children´s socio-emotional behavior during the transition from preschool to primary school. We collected qualitative teacher interviews from 112 teachers from five different countries—Australia, China, Finland, Japan and Spain. The research questions were: (1) How do teachers in the five countries perceive children’s abilities in expressing and regulating emotions. (2) How are children’s emotions linked to their family relationships? (3) What similarities and differences across countries exist in teachers’ perceptions of children’s emotions? Overall, the interviewed teachers considered children’s emotional skills of crucial importance in the first grade and emphasized the importance of teaching children emotional skills, emotion management and regulation. The teachers reported that children can be stressed, worried or anxious during the transition. The educators also reported that transitions in the family such as parental divorce, the birth of a sibling or the death of a family member can manifest in children at school as restlessness, excitement, sadness or instability. Similarities and differences in the emphasis placed on children’s emotions by teachers were found across the five countries. We interpret these results to reflect differences in teacher education, school culture, resources and teachers’ freedom of choice in the educational system in the different participating countries. These factors all impact on how teachers think about children and emotions.