Annette wrote::hohoho: at you having us all going!
Ben was in mediums from 3 months and not on the tightest setting either. So really really don't bother with a small, there is so little point, even on a small baby the mediums fit as Hanna says probably from about 8lbs and I think you can wait until they grow into that as they aren't the cheapest. I am gutted Ben has grown out of the medium now at 8months as they only lasted 5 months but I think the larges will last us a good long while and they are a fab nappy with a good resale value at the moment.
Blimey, Gracie is nearly 10 months and in the medium on the tightest, she must be sooooo skinny, she is just over 18lbs so I guess that is pretty wee!!!!