We used newborn nappies on the inside of the cast with all the tabs cut off with a larger crawler size nappy over the top of the cast. We found that we could actually reach the inner nappy at the back through the top of her cast which made it a lot easier for us to get it into the correct position. The cast got a little bit tighter as she got bigger, but nothing major, she was only in it for five weeks and we didn't have any growth spurts in that time.