We got these suits for a wedding.  I bought a 2T and a size 6.  The 2T was huge and the size 6 was almost too small.  The white shirt that comes with it is very thin.  The jacket and vest are great thickness but the buttons on them break really easy.  I've had to replace all of them on the size 6.  The pants are pretty thin so if you are in a cold weather climate I'd buy a bigger size and put something on underneath.