Answer: Fanning of the toes and dosriflexion of the big toe is an abnormal response called the babinski reflex. Its a neurologic relfex. Newborn babies are not neurologically mature and therefore show a Babinski response. Many young infants do this, too, and it is perfectly normal. However, in time during infancy the Babinski response should vanish completely.
Explanation:
Positive Babinski sign happens when stroking the sole of the foot, the big toe bends up and back to the top of the foot and the other toes fan out. This can mean that you may have an underlying nervous system or brain condition that's causing your reflexes to react abnormal. This abnormal response is a problem of the CNS normally the pyrmidal tract. In this case the baby is 18 months old and is not mature neurologically so this response is perfectly okay.
But if it persists after the age of 2 years or as an adult it should be considered as a problem.