It is well established that nutrition during the first 1,000 days of life can have a long-term effect on growth, metabolic outcome, and long-term health. We review the long-term anthropometric follow-ups of children with risk of later morbidity: (a) very-low-birth-weight (VLBW) infants who have birth weights <10th percentile of weight and receive fortified breast milk, (b) infants from developing countries who are breastfed according to the present recommendations but have low birth weight and length, and (c) children from developed countries who were enrolled in randomized controlled trials (RCTs) to test if breastfeeding and low-protein formulas can prevent from rapid weight gain and childhood obesity. VLBW infants can be appropriate, small for gestational age (SGA), or intrauterine growth retarded (IUGR). SGA and IUGR (due to placenta insufficiency) infants are born with birth weights <10th percentile of weight for gestational age (GA). We provided fortified breast milk until 52 weeks of GA to 31 SGA and 127 IUGR infants and followed up growth until 24 months. IUGR infants showed lower weight gain between birth and 3 months and had lower weight between 3 and 24 months (p < 0.05; ANCOVA). No significant BMI differences between SGA and IUGR infants were observed. It seems that IUGR infants receiving fortified breast milk need special attention, because without further improvement in breast milk fortification weight gain after discharge from hospital might be too slow. In developing countries, length and weight of breastfed infants during the first 2 years are strongly influenced by the respective anthropometric parameters at birth. Studies in the Gambia and Zimbabwe indicate that only breastfed infants with birth length and weight above the respective WHO 0 z-scores continue with adequate growth and have length and weight above the WHO 0 z-scores at 18 and 24 months. Prevalence of stunting and wasting in the overall Gambia breastfed infant population rapidly increases during the first year, peaks at around 3 years, but decreases thereafter. Long-term growth trajectories indicate later start of puberty and slow pubertal growth, but adult weight and height are not reached before 20-24 years. In adulthood, prevalence of stunting and wasting is much lower than during any period of childhood. Maternal risk factors, such as childhood marriage and poor nutrition before and during pregnancy, need to come into focus to improve birth length and weight and lower high stunting rates. Term breastfed infants from overweight/obese mothers and breastfed infants with rapid weight gain during infancy have increased risk of childhood obesity. Infants who are exclusively breastfed 4-6 months or receive low protein follow-up formulas (high-quality protein) grow slower during the first 2-3 years than infants fed high-protein formulas. During follow-up examinations at 5-6 years, they have lower BMI and obesity prevalence. Body composition measurements (DEXA) at 5-8 years in children who were breastfed and received low- or high-protein formula during infancy indicate that breastfeeding and feeding low-protein formulas are associated with lower gain of fat mass. Longitudinal cohort studies show that high-protein intake during the first 2 years results in higher BMI at 9 years and during adulthood. The studies presented indicate that breastfeeding but also other pre- and postnatal nutritional, epigenetic, and environmental factors influence growth trajectories and long-term health.