At birth, the baby's spine has a very rounded position and isn't mature enough to maintain itself vertically. The baby's musculature also has yet to develop enough to allow for it. This means that the baby needs to be kept in a more rounded position so as to take into consideration his inability to support himself in a sitting position. Verify that his knees are lifted up and that his bum sits at the bottom of the baby carrier. This position is often called the M position or crouched position. Ideally, the baby's feet would be pointing downward. By slightly tilting the baby's hips forward, his spine curves and ensures a proper position of his neck, which will allow his head to lean against his carer. The baby's spine and musculature will develop enough to allow him to maintain a sitting position around the age of 6 months.
We talk more about this topic in one of our articles. Read our article here.