Trying to buy sales but guessing sizes is so hard!! LO is 5.5 months and currently fits perfectly in 9 months carters and similar brands but 12 months aren't huge, especially after washing. He's 18lbs and been putting on about a pound a month at this point. He's 27.5 inches long. How long were your kiddos in 12 months. Should I but 12 or 18 months for fall? (It doesn't get cool here until November and never gets super cold.) I know growth slows...