Kid's Sleep Sack (Sleepwear)

Picture a sleeveless bag: fitted at the neck and armholes, roomy from the chest down, closed across the bottom. It exists because loose blankets, quilts and pillows are kept out of a crib for safe sleep, and a baby still needs warmth. Wearing the blanket answers both at once.

Two measurements decide whether one works. The neck and armholes have to be small enough that a baby cannot slide down inside. The body has to be wide enough at the hips that legs can bend up and out, which is how hip joints develop. Warmth is given as a TOG number, a thermal rating where higher means warmer: around 0.5 for a warm room, 1.0 for an average one, 2.5 for a cold one. Add a TOG and take a layer off underneath. A zipper running from the bottom up lets you change a diaper without lifting a baby's shoulders off the mattress.

Wearing one does not replace pajamas. A footed sleeper goes underneath and separates the legs, which a sack deliberately does not. A sack keeps working after a baby stands and cruises, and it retires once a child climbs out of the crib or moves to a bed. A swaddle, a wrap that holds the arms down against the body, is the stage before. It gets retired at the first sign of rolling. A sack leaves the arms free from the start, so it carries on after swaddling ends.

Crib sleepers from the newborn weeks to around age two are the group this was built for, especially in bedrooms that run cool and for babies who roll onto their fronts and lose covers. Once a child climbs out of the crib or moves into a bed, retire it, because a toddler who stands up in a leg-less bag falls. A heavy TOG in a warm room is the other mistake, since overheating is precisely what safe sleep guidance works to prevent.

Put two fingers in the neck opening before you buy. If the whole sack would slide over a baby's shoulders, it is too big. That is why sizes go by weight and length rather than by age. Wash sacks often on warm, and retire one when the neck elastic no longer springs back, because a stretched neck is the exact failure the design is meant to avoid.