Size six for a three-year old

I honestly think that this is insane. Reagan is wearing a size six and she's not even three and a half. She's close, but not quite there yet. How odd. She's about 38 pounds and almost 40 inches tall. I should probably measure her. Either way, she's solid kid. Tonight, I went to pick up another suit for her, because her 4T was even too small. Sigh... The sales person suggested a six because of her size. Um, I was really already shocked I had to get a five. I got it home and WOW - it fits!!!! My kid's growing up on me way too fast.