Final answer:
The Moro reflex or startle response should be present from birth until about three or four months of age and is key for an infant's neurological development. The absence of this reflex may indicate neurological issues and should be addressed by a healthcare professional. It is one of the many reflexes that ensure an infant's survival and is linked to cognitive development milestones.
Step-by-step explanation:
A child should have the startle response, also known as the Moro reflex, from birth until about three or four months of age. This reflex is an important indicator of neurological development and involves the infant suddenly spreading out the arms, bringing the arms back in toward the body, and usually crying, in response to a sudden loss of support or the sensation of falling. If a child does not exhibit the Moro reflex, it could be a sign of neurological problems, and medical consultation would be advisable.
The Moro and other reflexes like the grasping reflex, where the baby automatically grasps anything that touches the palms, are essential for an infant's survival as they help in maintaining close physical contact with the caregiver. These reflexes typically fade as the child develops and gains more control over their motor skills. In the context of cognitive development, around the time these reflexes dissipate, children are also reaching other developmental milestones such as developing object permanence and the onset of stranger anxiety during Piaget's sensorimotor stage.