Most parents will be able to differentiate their babies' cries within a couple of weeks. Language development is an ongoing process, and real words start sometime around 9 months of age. Parents always are very proud of their children's development achievements. Most of us can remember when our baby first sat up, rolled over, and took that very first step. But as exciting as these achievements are, most of these kinds of physical milestones are not very predictive of future intelligence.
Language is the one area of development that can indicate future success in school.
Language development is also important as it can be the earliest sign of a hearing problem or of autism and related problems. A parent is often the first person to have a concern about delayed language. Most doctors will take these concerns seriously. If language delays are investigated early, often the delay can be resolved with early intervention such as speech therapy or correction of hearing loss. Vocabulary builds so that by eighteen months, most children can say at least five words.