Background: Children’s mental health and well-being are major public health concerns that can influence learning, social life, and—in the short, medium, or long term—their future health. Until now, we lacked data objectively assessing the mental health and well-being of children aged 3 to 11 in the general population in France. To address this gap, Santé publique France conducted the “National Study on Children’s Well-being” for the first time in 2022 (Enabee 2022), with support from the Ministry of Health and the Ministry of National Education. Objective: The objective of this report was to estimate the prevalence of probable emotional difficulties, oppositional difficulties, and inattention/hyperactivity, the level of well-being, and to assess the use of healthcare services for mental health reasons among schoolchildren in the youngest to oldest kindergarten classes (ages 3 to 6) in mainland France, complementing previously published results on elementary schoolchildren. Materials and Methods: Enabee 2022 is a national descriptive cross-sectional study conducted in French schools. The probabilistic sampling design consists of three stages: schools, selected at random first; then up to four classes per school; and finally, all students in each of the selected classes. Data were collected between May and July 2022. For each child, one parent and the child’s teacher were interviewed using a secure online questionnaire or by telephone. Emotional difficulties, oppositional behavior, and inattention/hyperactivity were assessed using the parent and teacher versions of the standardized Strengths and Difficulties Questionnaire (SDQ); well-being was assessed using the parent version of the standardized Kindl (Kiddy-kindl) scale. Various indicators were calculated, taking into account the informant (parent or teacher) as well as the impact of these difficulties on the child’s life. The perspectives of the parent and the teacher were combined, according to the SDQ’s combination algorithm, to estimate the prevalence of these different types of difficulties experienced by the children. Results: Of the 438 randomly selected schools that had at least one student enrolled in preschool, 246 schools participated (56.2%). Of the 9,038 children eligible for the survey, a teacher questionnaire was completed and analyzed for 5,721 of them (63.3%) and a parent questionnaire for 3,785 children (41.9%). For 2,683 children (29.7% of eligible children), both a parent questionnaire and a teacher questionnaire were available. By incorporating the perspectives of both parents and teachers on this latter sample, 8.3% [95% CI: 7.1–9.6] of children aged 3 to 6 years exhibited at least one type of probable difficulty with an impact on their lives. More specifically, 1.8% [1.3–2.5] of the children exhibited probable emotional difficulties with impact, 5.9% [4.8–7.2] exhibited probable oppositional difficulties with impact, and 1.9% [1.4–2.6] exhibited probable inattention/hyperactivity difficulties with impact. Approximately one-third of the children who exhibited at least one type of probable difficulty with an impact on their lives had consulted a mental health professional (33.7% [26.4–41.6]) during the previous year in connection with these difficulties. The mean scores on the various well-being subscales ranged from 78.1 (family well-being) to 88.5 (emotional well-being), on a scale of 0 to 100. Discussion: The Enabee study represents a crucial first step in the epidemiological monitoring of children’s mental health, an area previously under-explored in France. After surveying parents and teachers, the study suggests that many children exhibit symptoms suggestive of oppositional defiant disorder (around 6%) and, to a lesser extent, emotional difficulties or inattention/hyperactivity (around 2%) as early as preschool, consistent with the limited epidemiological data available for this age group. At these early ages, adults’ expectations and assessments may differ; furthermore, behavioral and emotional problems can evolve rapidly: it is therefore important to exercise caution when interpreting the results. The aim is not to identify or stigmatize any particular child, but rather to obtain an epidemiological picture of the needs of children as a whole and, in the long term, to develop a more appropriate and relevant prevention policy that meets the needs of future generations. Assessing the mental health of very young children, based on input from multiple adult informants, is complex and requires further methodological consideration. Nevertheless, these initial indicators and the regular repetition of this study will make it possible to track their evolution over time and support national prevention and health promotion initiatives. Among these initiatives are, in particular, the public policies developed in response to the "First 1,000 Days" report on children, as well as the interministerial strategy for developing psychosocial skills among 3- to 25-year-olds, which aims, in particular, to improve children’s emotional regulation skills. The Ministry of National Education has also developed a policy within the framework of the Health-Promoting School initiative, along with measures to identify and support students experiencing psychological distress.