A sleep sack should fit snugly around the neck and shoulders.
So your baby can't wriggle down inside it. Sacks are sized by weight, not age — the maker's guide on the label says which.
1. Snug at the neck and shoulders, with armholes or sleeves. 2. Sized by weight, not age. 3. Never two sacks on top of each other, and no blanket over a sack. 4. Stop swaddling at the first signs of rolling, around three months.
Head and face stay uncovered for sleep. Check the chest or the back of the neck, not the hands.
Swaddling a newborn
Many newborns settle better swaddled. In the app a swaddle takes the sack's place for a baby of 0–3 months: a snug wrap, arms in, with a lighter cloth in a warmer room.
Red Nose says to stop wrapping at the first signs of rolling, around three months. From then on, a sleep sack.
Nothing else in the cot
The Lullaby Trust says no pillows, duvets or thick bedding, and no blanket over a sleeping bag. The sack is the bedding.
Never a hat for sleep, whatever the room.
Which TOG
Match the sack's TOG to the room, not the season.