Over the last 20 years, the effectiveness of positive psychology interventions for the development of the well-being of children and adolescents and the moderation of high levels of anxiety and depression in this population has been largely demonstrated. Emphasis has been placed on the promotion of well-being and prevention of mental health problems in the school context in order to foster, through positive psychology, the cognitive and socio-emotional development of primary and secondary students, e.g., by strengthening positive relationships, positive emotions, character strengths, optimism, and hope. However, little is known about the impact of these interventions on young children. This systematic review aims at examining the effects of positive psychology interventions on the well-being of early childhood children (<6 years old), both in the preschool education context with educators or teachers and also in the family context with parents. Several electronic databases were searched, and the findings systematically reviewed and reported by the PRISMA guidelines. Very few studies met the inclusion criteria (n = 3), highlighting the need for further research in this area. Indeed, all of the selected studies demonstrated the importance of positive psychology interventions with young children to promote positive aspects of development, such as gratitude, positive emotions, life satisfaction, accomplishment, positive relationship, or self-esteem. Limitations in the field are discussed.