I nursed all three of my children and my son is the only one who had trouble gaining weight. And it wasn't from not eating much! He has quite the appetite. His first 3-4 years he was only at 25% for weight. Finally got up to around 50% by the time he was 5 years old. He'll be six next month and he's still tall and thin. He can still wear some 2T/3T shorts. He needs a size 6 in pants for length but they have to be adjustable waist pants so I can make them smaller. He weighs 42 lbs now and he's just under 4 ft tall.