Ny nephew weighs 45 lbs which is what I've read is somewhat average (for his age). He barely grows out of his clothes, has had the same shirt for nearly a year (a very little shorter in the arms), mom buys the clothes snug but even so, they kind of hang on him. He is bird/elf like almost to the point of skeletal. His parents are both large people. Anyone else have kids like this? He seems otherwise healthy and is energetic to the point I wonder if he might be ADHD (he gets distracted easily, and is not so focussed on getting the calories in). My son was different in that I frequently had to buy clothes a size ahead although for the longest time he was tall and lanky (now he's just large which another matter altogether). It's been so long with my son I can't remember exactly what happened but my friends daughter, a year younger than him is about the same size (I think, judging by clothing size).