To the moms and dads out there: Raise your hand if your 12 month-old fits into size 12 month-old clothes.
I didn't think so.
Why on earth are baby/toddler clothes sized by months? My 17 month-old is perfectly average in size and weight yet barely fits into 24 month-old clothing. Is this the equivalent of women's sizing (you know, where designers cut clothes bigger than the true size, so you fit in a 4 when you're really an 8)? How is this of any use to anybody? At first, you get a little rush when you think that your child is bigger and taller than they're supposed to be, but after a few months you're on to their scam. Yeah, it's a psychological boost when I fit into a size small skirt (even if it's a lie and I know it) but I get nothing but irritated when I can't figure out my son's size. I've got better things to do than trying to remember if my son's an 18 month or 24 month size at Old Navy. Like going shoe shopping.
Aside: Gymboree/Janie and Jack run big (he can still wear size some size 12-month clothes from them). Old Navy/Gap? Their stuff is tiny - buy twice the age. How clever!
My proposal is this - why not size toddler-infant clothing by weight? Then you will know that this shirt will fit your child when he is between 20-30 pounds, for example. And if there is one thing a parent knows, it is the weight of their child. It's one of the least bothersome questions you get asked by total strangers. The pediatrician tells you the weight at each visit. Wouldn't that be easier?
Also feel free to discontinue "newborn" sizes. Shower gift recipients everywhere will thank you. It doesn't matter how many times a day you change a newborn, it is statistically impossible to get all the adorable newborn gift outfits on them before they outgrow them 3 days after getting home from the hospital. The onesies they gave me at the hospital were size 6 months, that should tell you something.