Dear Colleagues, Mental disorders significantly contribute to childhood disability worldwide, affecting about 15% of young people, with over half of cases emerging before the age of 14. These disorders constitute more than a third of patients' lives, leading to a roughly 13% reduction in life years due to premature mortality or to living in a state of compromised health (i.e., disability-adjusted life years (DALYs)). Despite being a global priority, the understanding of active ingredients for preventing and treating mental disorders remains limited. Short sleep duration, poor sleep quality, and circadian disruption are among the well-established factors impacting mental health. However, it remains unclear whether they act as risk factors, consequences, or even prognostic endophenotypes. Addressing this crucial knowledge gap, we are looking from researches worldwide that explore the intricate relationship between mental health and sleep disorders in childhood, particularly regarding externalizing and internalizing symptoms and their differentiation.