From birth, the primary caregivers of an infant are instrumental in supporting the development of the child's ability to communicate. As the adults respond to the child's cries and movements, the child comes to instinctively recognize the sound of the voices of those persons and to be sensitive to the tones used in vocalization.
As the child develops, s/he begins to recognize that certain sounds or sets of sounds result in positive reactions by the adults. Children may be taught sign language for use in communicating basic needs before oral communication is developmentally possible. Adults in the child's life support the learning of such means of communication by responding to answer the child's needs, thus reinforcing the child's appreciation of the use of the signs to obtain what s/he wants.
Oral communciation begins with the child attempting to imitate the sounds s/he hears and associates with persons who have provided positive interactions. Adults who model speaking to the child, adults who respond to attempts at vocalization, adults who provide positive reinforcement of the child's attempts help the child's development.