Ensuring the highest level of well-being of young children during the transition is a significant challenge in the context of early and preschool education, so this study focuses on the analysis of significant determinants of well-being of young children (socio-emotional well-being and resilience, strengths and difficulties and temperament) during transitions, from the perspective of educators whose determinants of well-being are also analyzed (optimism, life satisfaction, and personality traits). Quantitative research included self-assessment of personality traits and well-being of educators and assessment of children's behavior in the domain of their socio-emotional well-being from the perspective of educators. The descriptive analysis of the data determined the results on the level of well-being of both educators and children, and the correlation analysis enabled the analysis of the relationship between the well-being of educators and the well-being of children during the transition periods. Determinants of children's well-being were measured by three scales: Scale of socio-emotional well-being and psychological resilience of preschool children (PERIK), strength and difficulty questionnaire (SDQ) and EAS model of children's temperament, and determinants of educator's well-being also measured by three scales: Life Orientation Test (LOT), Life Satisfaction Scale (SWLS) and Big Five Inventory (BFI). As expected, educators rated children with more positive traits and positive behaviors, and lower undesirability with significant differences in children’s gender and age. Also, moderate to elevated levels of all determinants of educator well-being were found except neuroticism which was also to be expected. The course of adaptation was assessed as medium to low satisfactory, which makes a very important finding that should be investigated in more detail and reveal the causes of dissatisfaction of preschool teachers, as well as the finding that younger educators with less work experience have higher levels of neuroticism than their older colleagues. As assumed, individual determinants of children’s well-being are significantly related to the determinants of the well-being and personality of educators, which should be borne in mind when creating guidelines for improving preschool practice and professional development of educators.