Babies are born desperate to communicate. They already recognise their mother's voice and within a very short space of time have learned the rules of conversation. By the time they are five, children have sorted out the grammar of their mothertongue and can even have mastered a second language. Connie St Louis explores this incredible achievement by talking to children from birth to five years old. Producer Julia Durbin. E-MAIL: scirad@bbc.co.uk