Babies are born with several involuntary muscular responses to sensory stimuli, such as light or touch, which gradually disappear as a baby’s nervous system – brain, spinal cord and sensory nerves – develops. These are called primitive reflexes and include the following:

• Rooting and sucking reflex. It triggers newborns to turn their heads when their cheeks are touched (in search of food) and begin to suck on a pacifier, baby bottle or any object placed in their mouths.
  
  
• Tonic neck response reflex. This prompts an infant to extend the left leg when looking to the left, while the right arm and leg flex inward, and vice versa.
  
  
• Grasp reflex. It causes a baby to tightly close the fingers when pressure is applied to the inside of the hand by a finger or other object.
  
  
• Moro reflex. Also called startle response. It prompts an infant to suddenly throw the arms out to the sides and then quickly bring them back towards the body when startled by a loud noise or other stimulus.
  
  
• Stepping and walking reflex. When a supported infant’s feet are placed on a hard surface, the baby makes stepping motions.

Most primitive reflexes disappear in the child’s first few months. Primitive reflexes that persist beyond a certain age may be a sign of developmental delays or central nervous system problems. Infants are also born with a number of reflexes that continue throughout life, such as blinking, sneezing, coughing, yawning and gagging.

For a few weeks after birth, newborns continue to use the fetal position – fists clenched, elbows bent, hips and knees flexed, and arms and legs held close to the front of the body. A baby’s arms, legs and chin may tremble or shake, especially when the baby is crying or agitated. As the nervous system matures, this response lessens.

During the first two months of life, infants typically display limited movement of their extremities – mainly writhing and simultaneous opening and closing their hands. Between the first and second month, babies can usually lift and turn their heads when lying on their backs. However, a baby’s neck muscles cannot yet support the head. Any person holding a young infant must support the baby’s neck and head. It is also important to never shake a baby. Shaking a baby can cause a serious and sometimes fatal condition called shaken baby syndrome, which may damage the brain and delay normal development.

From about age 3 to 4 months, most of a baby’s primitive reflexes have disappeared or are beginning to do so. Infants can now roll from their backs to one side and can better control hand and feet movement, although they are still unable to coordinate grasp. Babies can grasp and shake toys that are placed in their hands, but cannot pick them up if dropped. They also typically attempt to grab dangling toys or other objects. At this age, babies begin to put objects into their mouths.

Many 3 and 4 month-old infants are able to raise their heads and upper bodies with their arms while lying on their stomachs. Around this time, babies can keep their heads up while sitting up (with support) because neck muscles are more developed.

From age 5 and 6 months, infants can grab larger objects like blocks and cubes, as well as pick them up if dropped. However, they have not yet achieved fine motor control of the thumb and index finger for grabbing. Many infants this age may be able to hold their own bottles, but only for short periods of time. Most babies can now completely roll over from the back to the stomach.

While lying on the stomach, 5- and 6-month old babies can push up with their arms to lift up the shoulders and head and look around or reach for objects. Around this stage, most babies are also able to sit alone without support for brief periods. Infants also typically display what is called a parachute reflex to protect against falling. This involuntary muscle response can be elicited by holding a baby upright then rotating its body quickly face forward, as if falling. The baby’s arms instinctively extend as if to break a fall.

From months 6 to 9, infants are typically able to sit steadily for long periods of time, especially when placed in a high chair. Most healthy babies are learning to crawl and may be able to pull themselves up – and remain standing – while holding onto large objects, especially furniture. Many infants are able to sit from a standing position with assistance. At this stage, most babies are also able to walk while holding the hands of an adult.

From months 9 to 12, babies often begin displaying a preference for the dominant hand when grabbing toys or other objects. They have better coordination of the thumb and index finger, which allows for a pincer grasp – grabbing small objects between the tips of these fingers. Most babies can also turn through the pages of a book by flipping many at a time and are generally able to finger feed themselves.  

Generally, older infants begin to balance better while standing without support and can also sit down unassisted. Most healthy babies usually begin taking steps or may even start walking without help by their first birthday.