Match My FlY Our baby onesies one-piece are made from 100% pre-shrunk cotton and are available in five different sizes. All baby onesies are machine washable. Our baby onesies are designed with comfort and durability in mind for both you and your little one. Crafted from 100% pre-shrunk cotton, our baby onesies provide a snug fit while withstanding countless washings. Plus, they come in five convenient sizes for a perfect fit at any age.