Is there a huge difference b/w size 12 mth and 18 mth baby boys'

[Hippoharbor]

Hi. THis is my first child and I have been wanting to order some clothing for winter that I found on sale. DS is only 19 wks currently, 25 inches, and ~15 1/2 lbs. He won't be 12 months until Feb. He is wearing 3-6 months currently in most clothes but wears a few 9 mth sizes (Ralph Lauren shirts). I am afraid that if I buy 12 mth size, he won't get much wear, if any, by the time fall/winter comes to St Louis or that the 18 mth size will be too big.

Any suggestions, please?

TIA
MIchelle

[Momof3Labs]

It varies by brand. Look at the growth charts at www.cdc.gov to see what size he'll be if he follows his current percentile. Then compare to the size chart for the brand clothes you are considering.