DD3 is in small itti bittis now and she's 5.2kgs now, but with skinny chicken legs. Just in case you're considering buying some smalls, I have the all in ones and the snap ins and the snap ins are a bigger fit around the waist - I guess because there is a little less bulk without the sewn in boosters. I find both styles perform the same so the snap ins might be better value with a longer life ITMS