High protein intake in young children is associated with excess gains in weight and body fat, but the specific role of different protein sources has yet to be described. The study aimed to investigate the role of different types of protein in the post-weaning stage on weight, BMI and overweight/obesity at 60 months. Intakes of animal, dairy and plant protein and a dietary pattern characterising variation in protein types at 21 months of age were estimated using a 3-d diet diary in a cohort of 2154 twins; weight and height were recorded every 3 months from birth to 60 months. Longitudinal mixed-effect models investigated the associations between sources of protein intake or dietary pattern scores and BMI, weight and overweight/obesity from 21 months up to 60 months. Adjusting for confounders, dairy protein intake at 21 months was positively associated with greater weight (46 (95 % CI 21, 71) g and BMI up to 60 months (0·04 (95 % CI 0·004, 0·070) kg/m2) and the odds of overweight/obesity at 3 years (OR 1·12; 95 % CI 1·00, 1·24). Milk showed associations of similar magnitude. A dietary pattern low in dairy protein and high in plant protein was associated with lower weight gain up to 60 months, but not overweight/obesity. Intake of dairy products in early childhood is most strongly associated with weight gain, compared with other protein sources. A dietary pattern characterised by lower protein intake and greater protein source diversity at 2 years may confer a lower risk of excess weight gain.