For many new parents, swaddling seems like the hardest thing you’ve ever done—until it’s time to stop swaddling. For this installment of our product evolution series, NYC Sleep Doctor Janet Kennedy, PhD and aden + anais founder Raegan Moya-Jones give us the rundown on how keep babies safe and warm in the crib, from swaddling to sleep sacks—and beyond.

StrollerTraffic: The perfect swaddle can be quite elusive. Where do parents tend to go wrong?
Moya-Jones: The most common mistake I see is a loose swaddle. There are four easy steps to swaddling, but the key to a tight swaddle is to hold the fabric close to baby when you bring the wrap across baby’s chest, so that you can pull it nice and tight.
Kennedy: Parents often assume that their baby doesn’t like the swaddle if he or she is fighting it or busting out. But before giving up on the swaddle, it’s a good idea to try a tighter one. Babies who resist it often sleep more soundly when swaddled correctly.

ST: Well in that case, what are the real signs that it’s time to lose the swaddle?
Kennedy: Most babies can benefit from being swaddled for the first three months.  Once a baby can roll over to his belly, I recommend getting rid of the swaddle. If the baby is starting to suck her thumb or hand, having access can help promote self-soothing. Also, I advise parents who are using cry-it-out sleep training methods to un-swaddle the baby. And finally, if even the tightest swaddle doesn’t stay on, then it’s safer to stop swaddling.

ST: Any tips for surviving the transition from swaddle to sleep sack?
Kennedy: Some people find it helpful to leave one arm out of the swaddle for several days before getting rid of it altogether. It can also help to start with one nap a day un-swaddled and gradually increase as the baby gets the hang of it. Once she’s successful at napping, the nighttime transition could be easier.
ST: And what about the sleep sack phase? How long does that last?
Kennedy: Sleep sacks are fine for the long term as long as the child is comfortable. Some babies move around a lot and a sleep sack becomes an annoyance.

ST: If a baby is “over” the sleep sack, but not ready to stay tucked under a blanket . . . what then?
Kennedy: Footed fleece pajamas will accomplish the same warmth without interfering with the baby’s repositioning during the night.

ST: Speaking of blankets, when is it okay to put a blanket in the crib?
Kennedy: To minimize the risk of SIDS, parents should wait until the baby is at least one year old to put a blanket in the crib. Babies don’t stay tucked in, so the blanket is really just a comfort object until the child is well into the toddler years.