Answer: This repeating of syllables is called BABBLING.
Explanation: Babbling is a stage in the development of language in Children in which a child appears to be demonstrating with sounds by producing uttering sounds of language without any recognizable words.
This starts a little while after the birth of a child and passes through several stages until the child utterance become speech like.
Babbling can be seen as a forerunner to the development of language.