Talking to babies. Babies learn from their interaction with us, and the world around them. They learn by imitating us as well. Most experts suggest that multilingual children learn the nuances of different languages by the time they are 3 years old, after 3 our brain has a bit more dificulty in learnig different languages, any conversation is a valuable learning tool for our children. Tv will not help their speech.
Learning. It helps baby learn receptive and expressive language skill, it to a degree models behavior, and helps the child enter the world around them.
Immitation. Babies and children learn to speak through imitation. They watch their parents and other caretakers speak and try to do the same. One can often see a baby trying to mouth the words he just watched his mother say.
Helps learning. Babies grow and develop their language, personality, and social skills through interacting verbally and nonverbally with others. Talking with ones baby is important. Playing with the baby is also important.
Pattern recognition. Conversation helps in a whole bunch of ways. For one, babies will start to learn words, sounds and sentence structure from hearing speech. If that speech is directed at them, they pay more attention, and they know from learned social cues they are supposed to answer back, encouraging vocalization. It also builds social contact and thus self esteem for the child.