The Prevention of Overweight in Infancy (POI) study is a four-arm, randomised controlled trial assessing whether extra education & support around sleep, breastfeeding, diet, & physical activity reduces the number of children showing excessive weight gain over the first two years of life. This application proposes follow-up at 3.5 & 5 years of age in an anticipated 600 of the original 805 families, to determine the sustainability & long-term consequences of this approach. Further measures of growth (anthropometry, DXA), diet (questionnaire), sleep & physical activity (accelerometry) will be obtained at both time points. Novel additional measures include analysis of the gut microbiota & its relationship with obesity in young children, & the use of inclinometers to measure sedentary behaviour. If successful, POI strategies are designed to be incorporated into New Zealand's Well Child Health services to make a significant impact on overweight & the long-term health of NZ children.