They’re called a primitive reflexes, and they are reflex actions within the central nervous system that are exhibited by babies, yet not part of the neurological makeup of adults.
In response to different stimuli, different reflexes will occur mostly for the purpose of survival. For example babies when hungry and touched by another person will display what is known as the "rooting reflex" which helps them instinctively find the mother’s nipple to breastfeed.
The "Moro reflex" results when a baby’s head is moved. The reaction all children will have is unconsciously extending their head and legs, their arms will jerk up and out with palms up and thumbs flexed and the baby will cry loudly.
These reflexes disappear as we age because the frontal lobes slowly faze them out. Unfortunately, those with atypical neurology retain some primitive reflexes such as cerebral palsy, and improper fazing out can lead to dementia, traumatic lesions, and strokes.