My daughter is 3½ and wears 3T in clothing. So, after reading the reviews here I ordered this swimsuit in 4T... and it's still small. I think it'll work once she's in the water (when it stretches a little), but if I were to order it again I'd order a 5T. In other words, it differs TWO sizes from what she normally wears.

The quality seems to be excellent though...

really good quality and value, but much too small for my daughter. Embarrassingly so!!!

runs very small.  I purchased this and it was on the small side to begin with and then I washed it that first night and now its useless.  my daughter cannot use it. its now so small its uncomfortable.

Quality looked and felt great but my 4yr old who wears a size 4 couldn't even get it past her hips.  It looked like it "might" fit an 18th month old and I mean this wholeheartedly.  I have a 24month old son with several friends in the same age. I gave it to one of his little friends who is 18 months old and I'm still waiting to hear it if even fits her.

This suit was WAY to small to be marked a size 4.

A very nice suit, except it is way too small.  I wish I had returned it, but it is now too late since they already wore them.  I had hoped the suit would loosen up in the water.  It doesn't.
I got a 6x for my six year old and it just barely fits my four year old.  Really too bad.

I love the color, is exactly as it looks online and it feelg very good, my daughter loves it.