Once babies start to learn to stand, walk, and sleep independently. At this stage, your baby will be mobile. These sleep sacks are usually easy to wear. So babies can wear it more comfortably and crawl or walk more freely. No baby likes to be tied up. And we use high-qualified, two-way YKK zippers to keep the baby safe. Parents can change the sleep sacks for their babies easier. Besides, Kaiya Angel independent sleep sacks can be worn with baby rompers and baby bodysuitsperfectly.