If you don’t know the baby’s size it’s always a good idea to size up as a rule of thumb. However, when it comes to sizing for a bodysuit for a child it’s best to check the sizing chart provided by the manufacturer and measure your child before buying. It is tempting to size up, so your child can grow in the bodysuit and you save money, but a too large bodysuit can create uncomfortable gaps or wrinkles whereas a too snug bodysuit can restrict your child’s movements. A bodysuit should always be comfortable and snug.