Given that one in three New Zealand children are overweight or obese, research aiming to address the global obesity pandemic has increasingly focused on opportunities for prevention in early life, particularly in the ‘first 1000 days’ (from conception to 24 months of age). Our recent POI trial demonstrated that children who received a brief sleep intervention in infancy had only half the risk of obesity at 2 years of age as children who did not receive the sleep intervention. More importantly, these benefits remained at 5 years of age, even though no intervention had occurred for at least 3 years. This follow-up will determine the long-term sustainability of this brief intervention, which has the potential to dramatically reduce obesity risk in children. More than 700 POI children will be invited to attend the 10-year-old follow-up to measure growth, body composition, sleep and physical activity patterns, eating behaviour, health and wellbeing.