Not all children have the same needs. These needs will change as the child continues to grow. Newborn babies and very young children have very little neck, spine and muscle strength. They start gaining strength as they grow.
Therefore, a child car seat designed for babies cannot be the same as one for a 4-year-old child. This is why there are specific child restraint systems for babies on the market, such as Group 0, 0+ and i-Size child seats up to a certain height, often 85 cm.