By using a special form of language, adults help babies learn a sense of mutual trust and the importance of taking conversational turns. Babies also learn that paying attention to the other person enables them to respond to what's been said. A caregiver might use very high pitch and vary the range of pitch from high to low. She also should speak slowly, distinctly, and repeat words and phrases. Just because babies don't use formal language doesn't mean that they don't understand exactly what we're saying.
Children understand a lot of what's said long before they can reply in words.
Talking about babies in front of them and assuming they don't understand conveys a sense of disrespect to them. The most vital thing to stress about language development is the value of conducting a true conversation with children. This means listening with sincere interest, responding in a way that will enhance and continue conversation, and allowing children time to formulate their ideas and answers. Waiting for replies is one of the most important things we can do to encourage language growth. Slow down and take the time to listen to what children have to say.