Toddlers at the age of two who have a vocabulary of less than 50 words are at risk of developmental problems that can persist into later life according to scientists who have devised a speech test for young children.
Most two-year-olds have a vocabulary of between 75 and 225 words but a minority of less than 15 per cent are "late talkers" who do not use more than 50 words, said Professor Leslie Rescorla of Bryn Mawr College in Pennsylvania.
A study that identified late talkers at the age of two found that at the age of 17 they continued to perform less well in language tests compared to other children, even though they had no other developmental problems, Professor Rescorla said.
"By the time they got to school most of them were performing in the average range. That was the good news. But at the age of 17, these children performed significantly less well on all the language measures we gave compared to a group of children of the same age and backgrounds," she said.
"It looked as if what we were picking up at the age of two was a sub-clinical but enduring relative weakness in early language development and later language skills," she told the American Association for the Advancement of Science in Vancouver.
One of the best ways of identifying these children is for parents to monitor which words they are using. Late talkers tend to only use the 50 most common words used by all toddlers at the age of two, she said. "We can identify these children. Not all of them go on to have problems, but many of them do. We can identify the 50 most common words used by two-year-olds and we find that generally those are the ones that late talkers are using.
Many late talkers at the age of two can catch up with their peers, but if they continue to use only 50 words at the age of three and above, this is a sign that there could be more serious underlying problems that require intervention, she told the meeting.
"Children need to have people talk to them for them to acquire language. Not that they learn nothing from TVs and videos, but they really need language partners," she said.
Nan Bernstein Ratner, professor of hearing and speech sciences at the University of Maryland at College Park, said that early intervention with children who are late talkers does help.
"Deciphering who are the late talkers and following them up may be very important in identifying children who will later on be the children who will have difficulty learning to read. And we know that if we have children who cannot read, we have children who will not succeed in society," Professor Bernstein Ratner said. "We know that early intervention works," she said.
Some of the 50 most common words spoken by two-year-olds include: mommy, daddy milk, juice, hi/hello, ball, no, yes, dog, cat, nose, eye, show, banana, car, hot, thank you, shoe.