AimTo identify the symptom burden in children and adolescents with post COVID-19, a validated and reliable instrument is needed, particularly to assess symptoms and their impact on the child. The aim of this study was to describe the development, validation, and reliability of the Post COVID-19 in Kids Questionnaire (POCOKIDS-Q), which was designed to assess post COVID-19 symptoms in children and adolescents.MethodsThe POCOKIDS-Q was developed based on literature, clinical experience, and questionnaires for adults with post COVID-19. The linguistic validation involved 9- to 17-year-old children. Children and adolescents with the onset of post COVID-19 symptoms were asked to complete the final version through a web link. Exploratory and confirmatory factor analyses were performed to identify a factor structure that explains the covariances between the variables.ResultsThe link to the POCOKIDS-Q was opened 324 times and fully completed by 213 (66%) children and young adults (median age 14 years) with post COVID-19 symptoms. Confirmatory factor analyses revealed four significant and correlated factors: brain fatigue, cognitive impact, physical impact, and emotional impact. The explanatory power of the factor model is high.ConclusionThe POCOKIDS-Q is applicable for assessing post COVID-19 symptoms in children and young adults.