It is normal for babies to have their legs raised when lying down. Normal motor development in the supine position can be shown as follows: 1, 3-4 months of age when the legs will be raised away from the bed; 2, 4-5 months of age when the thighs are flexed, hands can touch the legs; 3, 5-6 months of age when the legs are further raised, a small part of the buttocks out of the bed, hands can grab their feet; 4, 6-7 months of age can take the feet to eat into the mouth. This motor development pattern follows the developmental sequence of the human body, that is, the human center of gravity from low to high and the contact area between the body and the bed surface from large to small.