Sometime during the third or fourth, babies movements become intentional, voluntary and controlled, as the dominance of the reflexes continues to wane. When babies want to get hold of something, they now use their acquired skills to reach it: extending the hand, striking the object, or grasping it and bringing it to the mouth...
Babies can now hold their head steady independently , and they enjoy lying on their tummy for longer periods at a time - by now they can raise their head and chest while leaning on the hands.
Babies now try to roll to the side - an effective way to learn how to shift weight from side to side, which makes for excellent practice for rolling over.
Pre-crawling movements also appear now: babies move from side to side, and inch forward or backward.
Babies come up with some incredibly creative ways to be mobile: be it using the head as a pivot to move the rest of the body, or utilizing the tummy as an axis on which to turn from side to side - these are all effective training methods for moving forward.
Sitting and Spine
By the age of 6 months,
when placed in the sitting position, babies may be able to remain seated without falling to the side. This means that the muscles and spinal column are developing and becoming stronger. However, avoid placing babies in the sitting position for too long so as not to exert excess pressure on the spinal column. It is best to allow babies to move to a sitting position on their own - they will do it once the spinal column is mature enough to bear the weight.