Delirium is a syndrome characterised by an acute and fluctuating alteration in cognition and awareness. It occurs frequently in children with serious medical illness, and is associated with adverse outcomes such as increased length of hospital stay, duration of mechanical ventilation, hospital costs, and mortality. Delirium-especially the hypoactive subtype-is often overlooked by paediatric practitioners, but can be reduced by mitigating risks and effectively managed if detected early. Non-modifiable risk factors of delirium include young age (age <2 years), cognitive or neurological disabilities, need for invasive mechanical ventilation, severe underlying illness and pre-existing chronic conditions, and poor nutritional status. Routine bedside screening using validated tools can enable early detection of delirium. To reduce delirium in hospitalised children, health-care providers should optimise the hospital environment (eg, by reducing sleep disruption and keeping the child stimulated during the day), improve pain management, and decrease sedation (particularly use of benzodiazepines).