Baby Sleeping Bag is a wearable blanket that will keep the baby at a comfortable temperature through the night. These will remain safely uncovered. The main purpose of a sleep sack is to keep your baby's crib free from any loose blankets. Baby Sleeping Bag using a wearable blanket such as a sleep sack or a sleeping bag to keep the baby warm. These can be used from birth if fits. These are helpful in the first few weeks to prevent them from startling awake as soon as you put them down.