Childhood cancers are rare diseases with about 1700 cases below 15 years of age diagnosed in France each year. Although more than 80% of patients are now surviving more than 5 years, cancer remains the leading cause of fatal diseases between the ages of 1 and 15 years. The difficulty of diagnosis is partly due to their rarity but also the apparent banality of initial common symptoms. In industrialized countries, it is rare that an extension of time before diagnosis is associated with decreased survival; at the opposite, this period may be associated with the need for more extensive treatments leading to a greater risk of sequelae. Such delays also have a negative impact on the trust of the child and family with the medical community that may sound on the quality of essential therapeutic alliance. Learn how to diagnose these diseases, prescribe or repeat further explorations in case of persistent symptoms and suggestive signs and possibly refer these patients to a specialized paediatric oncology team is necessary to avoid excessive delay before diagnosis. In addition, it is also important not to ignore situations where these cancers are discovered in emergency situations: vital distress may require concerted management between intensive care and specialized paediatric oncology teams. Authors propose a focus on potential diagnostic pitfalls and emergencies during the initial management of children with cancer and the consequences of any diagnosis delays.