A study conducted by UK and US scientists based at King's College London, and Brown University, Rhode Island, explains why young children are good at learning two languages.
Dr Jonathan O'Muircheartaigh, who led the study, told the BBC: "Since our work seems to indicate that brain circuits associated with language are more flexible before the age of four, early intervention for children with delayed language attainment should be initiated before this critical age."
On average, 12-month-old babies have a vocabulary up to 50 words but, by the age of six, this number increases up to about 5,000 words. After that, children's vocabulary will continue to increase, though not as easily and fast that during the early years.
A very good reason to speak and read a lot with your babies and toddlers.