Transitional periods in children's lives are extremely challenging and significant, so it is crucial to systematically investigate their significant determinants. At the same time, it is interesting to focus on the comparison of established determinants between children of early age and children of primary school age. Educators and teachers have had to self-assess their own well-being and then the well-being of children during the transition. After the descriptive and correlational analysis of the collected data, a comparison of the well-being of children during the transition was conducted. The aim of this paper was to determine the significant determinants of transition in children of early age and children of primary school age and to carry out comparative analyses. A descriptive and correlational analysis was carried out, separately for the sample of early and primary school age. The research was conducted on a convenience sample in which children of early age (N=201), children of primary school age (N=152), educators (N=17) and teachers (N=13) participated. The paper analyzes the determinants of social-emotional well-being and resilience of children of early and primary school age and their connection with satisfaction, cooperation and difficulties during adaptation. The research has proven that there is a statistically significant connection between a higher level of social-emotional well-being of early and primary school age children with a lower level of difficulties during adaptation, a higher quality of satisfaction during adaptation and a higher quality of cooperation with parents and with a higher well-being of educators/teachers. It was also confirmed that children of primary school age have a higher level of social-emotional well-being and resilience than children of early age. The established results will provide useful implications for practice in early and preschool education institutions and primary schools.