I'm not the best person to ask, but I have read from the ladies here that sized nappies are better for a better fit. I have only a few sized nappies but mostly OSFA as I have an 18 month old and another on the way and I wanted nappies to do them both. But looking at the ones I do have they would fit from birth to toilet training as they have fold down bits for n/borns and then graduated snaps for bubs getting bigger to eventually just using the nappy as it is when they are full grown. In saying that I am going to use bamboo prefolds (rectangles of soft bamboo fleece folded) with a nappy cover for the first while with the new baby as they will be smaller, and then once baby has put on a kilo or two, use the OSFA nappies. I mostly chose OSFA for financial reasons..