I am looking at buying my niece a fall themed outfit. I found one that I like, but I can't decided what size to get her. She is 4 1/2 months old and weighs a little less than 15 lbs. The sizing chart says 3-6 months is 12-17 lbs and 6-12 months is 17-22lbs. I want her to be able to wear it up until around Thanksgiving when she will be about 6 1/2 months.. I think I should get the 3-6 months, but I am not sure.

Here is what I want to get:

http://www.gymboree.com/shop/dept_item.jsp?FOLDER%3C%3Efolder_id=2534374306281434&PRODUCT%3C%3Eprd_id=845524446030233&fit_type=Regular&ASSORTMENT%3C%3East_id=1408474395917465&bmUID=1380420222914

http://www.gymboree.com/shop/dept_item.jsp?FOLDER%3C%3Efolder_id=2534374306281434&PRODUCT%3C%3Eprd_id=845524446030215&fit_type=Regular&ASSORTMENT%3C%3East_id=1408474395917465&bmUID=1380420395969