Quick question. LO is 3 months old now, will be 5 months old on halloween. She was born 8 lbs 10 oz and now weighs about 12 lbs. She is in 3-6 month clothing, which fits her but not tightly.

I would like to get going on her halloween costume and found the perfect one-piece for the base of (she'll be a cat).

http://www.gap.com/browse/product.do?cid=95686&vid=1&pid=668621002

Question is, what size do you think I should order? 3-6 month, or 6-12? Does baby gap run large or small? (We have very few of their pieces so I'm not sure.) I could wait but also don't want it to go on sale and sell out, since it was surprisingly hard to find a plain grey footed romper, and one that's fuzzy (bonus! I didn't expect to find that).