As several other reviewers have mentioned, the sizing for these costumes is off.  The 3T/4T  fit my 2 and a half year old pretty well who is small for his age, 34 inches tall and 30 pounds.  The booties fit his shoes which are currently a size 7.  The size small (6) fit my 3 and a half year old a little snug between his legs, 40 inches tall and 38 pounds.  Those booties stretched to fit my son's shoe size of 11 but probably wouldn't stretch any larger than that.  They were both able to wear a layer of clothing (sweat pants and sweat shirt) beneath the costume which made them snug all around.  Material is thin and stretchy.  Visibility through mask didn't seem all that great to me, but my kids claimed they could see fine.  Overall a decent costume for the price, but I took a star away for the poor sizing.  This may not be durable enough to make it through another Halloween, but it does make for a super cute costume.  Thank you to everybody who reviewed this item so I was able to order the right size.  Hope this review helps others too!