My son is 4 yrs old. 46lbs and almost 4 feet tall. He normally wears a 5/6 in clothes. He is very long and slim so I was concerned the pants would be too big. I ordered a 5 and I couldn't be happier with the purchase!! The suit looks like it was tailored for him! I love that they have the elastic adjustable waist band so you don't have to get them taken in!! It is not a navy blue, a shade or so lighter. I wanted navy but it looks so good I don't even care! I am so satisfied with this purchase and will be ordering from them again!