Dehydration is a significant cause of morbidity and mortality in children worldwide. Infants and young children are vulnerable to dehydration, and clinical assessment plays a pivotal role in their care. In addition, laboratory investigations can, in some children, be helpful when assessing the severity of dehydration and for guiding rehydration treatment. In this interpretation, we review the current literature and provide an evidence-based approach to recognising and managing dehydration in children.