I'm a FTM trying to figure out what clothing sizes to get for baby. I am looking to order some clothes from baby gap & am wondering how the sizes run? Do the 0-3 month clothes fit the average sized newborn or should I get the up to 7 lbs size? Just wondering if the up to 7 lbs could be easily stretched to fit babies over that weight. Also, wondering how the Carters brand runs. Thanks!