Background: The COVID-19 quarantine has affected more than 860 million children and adolescents worldwide but, to date, no study has been developed to examine the psychological impact on their lives. The present study aims to examine for the first time the emotional impact of the quarantine on children and adolescents from Italy and Spain, two of the most affected countries by COVID-19.Methods: 1,143 parents of Italian and Spanish children aged 3 to 18 years completed a survey providing information about how the quarantine affects their children and themselves, compared to before the home confinement. Findings: 85.7% of the parents perceived changes in their children´s emotional state and behaviors during the quarantine. The most frequent symptoms were difficulty concentrating (76.6%), boredom (52%), irritability (39%), restlessness (38.8%), nervousness (38%), feelings of loneliness (31.3%), uneasiness (30.4%), and worries (30.1%), and Spanish parents reported more symptoms than Italians. As expected, children of both countries used monitors more frequently, spent less time doing physical activity, and slept more hours during the quarantine. Furthermore, when family coexistence during quarantine became more difficult, the situation was more serious, and the level of stress was higher, parents tended to report more emotional problems in their children.Interpretation: The quarantine impacts considerably on Italian and Spanish youth, reinforcing the need to detect children with emotional and behavioral problems as early as possible to improve their psychological well-being.