1-2T runs towards 2T, 2-3T runs towards 3T, and other appear true to size. They are versatile though as well. They are cute fitted and even tea length but also cuter looser and longer.
A child around 37 inches and 35 lbs. prefers the 2/3T. Another child approx. 53" 51 lbs. liked the 6/7T.