We recommend purchasing the size that matches your baby’s current size. Excess material can bunch up around your baby’s nose or mouth and suffocate them. this would in effect be counterproductive to the idea of the sleep sack. It is supposed to be a form-fitted covering that does not pose a hazard or problem for the child to be entangled in. with a larger size for growth, you are defeating this intention and increasing the risk of problems. You should have plenty of wear with the correct size that is made for the child.