Almost all group 0+ infant car seats come with a newborn insert. These are either a 'head hugger' and cushion (which is under the baby to lift them up) or just the head hugger on its own.
The purpose of the car seat newborn insert is to provide additional support and padding to a newborn baby when they are using the seat. The inserts also help ensure that babies fit in the harness, so they can be properly strapped in. The head hugger helps support the baby’s head, and if your seat comes with a cushion, it will lift the baby up to allow them to lie in a more natural position and will help prevent them becoming ‘scrunched over’.
As time goes on and your baby grows, the newborn cushion and head hugger can be removed; this is generally between 5-6 months of age.
When you remove the cushion from under the baby, it will ‘drop’ them down in the seat, giving them more room to grow. When you remove the insert, make sure that the harness straps are still level with or just below your baby’s shoulders; you may need to re-adjust the straps to fit your baby properly.