The Prevention of Overweight in Infancy study investigated whether education and support around sleep, physical activity, and diet could reduce excessive weight gain in the first two years of life. The analysis presented here assessed weight at 24 months postpartum and growth from 6 to 24 months. 802 mother-infant pairs were randomised to: 1) FAB – food, activity and breastfeeding (8+ contacts), 2) Sleep – prevention and treatment of sleep problems (2+ contacts), 3) Combo – both interventions (10+ contacts), or 4) Control. All groups received standard government funded “Well Child” care (7 contacts). Anthropometric measurements were obtained at 6, 12, 18 and 24 months postpartum by trained measurers blinded to group allocation. Rapid and extremely rapid growth were defined as a change in BMI z-score > 2/3 SD (World Health Organisation definition) and > 4/3 SD respectively. 84.5% (n = 678/802) of participants were followed up at 24 months with 40.1% having BMIs ≥ 85th percentile (n = 272). Among those with both 6 and 24 month data, 53.9% (351/651) showed rapid growth with 148 of these showing extremely rapid growth (22.7% of the sample). There was no difference between intervention groups for rapid growth (p = 0.892) or extremely rapid growth (p = 0.630) compared to normal growth. Similarly, there was no intervention effect on those classified as overweight at 24 months who also displayed rapid or extremely rapid growth (p = 0.936 for rapid growth, p = 0.485 for excessive rapid growth) from 6–24 months. Our results indicate it is difficult to modify excessive growth.