Unable to name simple words like cup or toy they will drag their teachers to objects to name them by touching, use facial gestures to say yes or no, or simply grunt. Faced with not being able to make themselves understood, they can throw tantrums of frustration.
Without precious language skills they risk a slow start to their education, which in the long term could penalise them academically.
Expert estimates suggest that around 375,000 of all pre-school and school- age children have some form of speech and language difficulty . Of these only about 10,000 will have any medical reason for the problem. Boys are four times more likely to be affected .
Afasic (the Association for All Speech-Impaired Children) says that on the evidence of the number of cases being referred to it by schools, social services and the health professions, incidents of language delay are "going through the roof".
"Speech and language difficulties are the most common of all pre-school and nursery problems," says the Chief Executive of Afasic, Norma Corkish. "Playing and talking to children is vital in the development of their speech and language - and in some families that simply isn't happening."
"Children are no longer being talked to so much," says Dr Loretta Light, a consultant community paediatrician who works in the Lichfield area of Staffordshire. "What I and many others in my profession are seeing is more and more children who have problems in all forms of speech - coupled with demanding and aggressive behaviour."
"I believe the problem does often lie in the home. Children are given toys that do things rather than toys to which they must do things. There's a lack of imaginative play - and in many homes there's often the constant noise of the television, which inhibits direct conversation children can learn from. I often go into people's homes in the course of my job and have to say, 'Could you turn the television off so we can speak?' "
Liz Jepson, from the Royal College of Speech and Language Therapists, says: "Increasing numbers of children are being referred to us at the age of two and a half to three, by parents who say, 'He just won't talk.' The simple answer is that some children are not getting enough stimulation."
Olwyn Gunn, education secretary of the National Association of Schoolmasters/Union of Women Teachers, who was the head of a primary school in county Durham for 12 years, says: "Children are spending more time in front of the television - and that kind of language washes over them. Children used to come to school knowing nursery rhymes, which are essential for early language because of the rhythm of repeating words and sounds. But now TV has taken over from books - it's much simpler for children to watch television than go through a book and talk about the pictures.
"You cannot ignore the issue of more women working. It's a change that I applaud in many ways, but what it has done is limit the amount of time available for mothers to be with their children and teach them how to talk."
Jackie Miller, general secretary of the Professional Association of Teachers, says speech problems are happening to children in all social classes. A survey carried out by the association, which looked at the effects on children who were allowed to watch TV and play with electronic games for long periods of time, found that this kind of "electronic child-minding" made them far less likely to be academically successful than their peers.
Says Ms Miller: "Secondly there is the issue of poor child-minding. Some parents are leaving their children with child-minders who aren't trained and who are failing to give the children in their care sufficient stimulation.
"Finally some middle-class children are not spending enough time with their parents - they're put in the care of a foreign au-pair who can't speak English very well and so these children have poor linguistic development," she says.
But intensive work with children and families on speech does make a difference. The Family Literacy project targeted parents and children aged three to six who all had poor literacy skills.
Special teams of tutors worked with the parent and child separately using books and videos - and then brought the two together so parents could see how they should read with and talk to their child. At the end of 96 hours of tuition over 12 weeks they found there was an marked improvement in both the child's and parents' basic literacy. Now the project has spread to 360 schools, which are receiving grants of up to pounds 5,000 to employ tutors to work with parents and low-achieving children.
Afasic is currently part-sponsors of a project which shows parents how they can communicate with their children better. Families have experienced a reduction in stress levels and better child behaviour.
Parents in the project are shown how to communicate with their children in ways many other parents do without even thinking: talking to their child about their day in a quiet atmosphere, going through a book, talking about the pictures and listening carefully even when their child struggles to talk to them. Some don't realise it helps to ask a child to pick up objects and identify them - and many parents across the social spectrum brush their children off when they try to talk to them.
"Simple things make all the difference," says Olwyn Gunn. "Pointing out things on a walk. Asking the child to identify objects when you're at the supermarket. Turning off the television and getting out a book. Making time to talk and listen even when you're busy."
'Some can't even ask to go to the toilet'
"Hello, Amy - would you like to do some drawing today?" Diane Wells, head of the nursery at Dumolo's, a primary school (left) on a bleak Midlands housing estate in Tamworth, Staffordshire, waits for a response. A rapid eye movement sideways and a blink. The answer is "yes".
Amy is one of 20 children from a morning session of 50 who have speech and language difficulties. Amy communicates through gestures rather than speech, although there is nothing medically wrong with her. She is one of thousands of children in Britain starting nursery at three-and-a-half with almost no basic vocabulary.
"Some of our children don't know the words for "cup", "spoon"and "toilet", says Mrs Wells. "Instead of teaching them about colours and shapes, we're teaching them the basics of communication.
"When they first start nursery, many of the children communicate by tugging, pulling and pointing. Instead of saying, "I want the toilet," they will lead a teacher there. If they want a toy, they will physically pull the teacher towards it - and if the teacher then tells them they can't have it for some reason, they can't understand and the frustration of not understanding spills over into anger."
The majority of these children do not have physical problems causing their speech delay. "The problem is stimulation," says Mrs Wells. "They simply aren't being taught how to talk at home. Most of our parents are very caring and loving - but there is less talking to children, fewer nursery rhymes being sung, less reading to young children.
"Many of our children have young single mothers and they don't realise that a child must listen to them talking to learn about language. Many parents use the television to keep their children entertained - but they don't realise that at the pre-school age, language on the television just washes over them - it isn't direct and simple enough for them to take it in.
"Some of our children communicate in a series of grunts, or else everything is 'the thingy' - and they find it very hard to learn names. We constantly get called 'teacher, teacher', rather than our names.
"Every day I sit by the door to say 'hello' to the children as they come in. I only get a response from about half of them," says Mrs Wells.
When the school spots a child with a problem, the parents are called in, and often it is the first time they have heard that their child has a problem with language.
"They say, 'but she talks at home,' or, 'I can understand her,' but they don't realise that they've had three years to learn how to break their child's code, and that other adults can't.
"Children need to listen in a quiet atmosphere to other people, ideally their parents, talking to pick up language. But in their homes the television is often on all the time and there's little direct conversation.
"Many of our mothers have had their children young - and they've missed out on the socialising that normally goes on at that age with their peers. They're trying to catch up on that now, and they'll talk to their friends, excluding the child.
"What worries me most is that for some of our children, school is the only place where adults speak or listen to them."
From speechless child to chatterbox
John Hills has a four-year-old-daughter, Megan, who attends Dumulo's nursery. At her three-year assessment she was found to be 12 months behind in her speech development.
"We knew she was very quiet, but because she was our first child we didn't realise there was a problem. Both my wife and I work, and my mother- in-law looked after her. I think there was a problem with the age gap. We also let her watch loads of videos - she loves all the Disney films and we didn't think there was anything wrong in letting her sit in front of them for a long time. We've been told by the school that we have to stimulate her mind more. We spend more time playing and talking to her. We all sit down together and say nursery rhymes and ask her to pick out objects and tell us what they are, and we read books to her. Life is hectic but now we know that we have to make time for her and she's come on in leaps and bounds - she's a real chatterbox now."
IS YOUR CHILD A GOOD COMMUNICATOR?
This parents' guide is issued by the Royal College of Speech and Language Therapists. Children's development varies widely, but these are the average achievements a parent can expect from a child.
18 MONTHS: Points to familiar objects and people on request. Understands simple requests, such as "Pick up your teddy." Can use at least 10 words. Tries to copy new words. Talks a stream of nonsense to him/herself.
TWO YEARS: Understands requests to point to parts of the body. Acts on simple commands, such as "Put the paper in the bin." Can use at least 20 words. Joins two words together, such as "want drink".
TWO-AND-A-HALF YEARS: Understands simple short stories and conversation. Uses three words together. Begins to ask questions. Joins in rhymes and songs.
THREE YEARS: Understands words like "in", "on" and "under". Can use four to five words sentences which most people can understand. Asks"what", "where" and "who".
FOUR YEARS: Uses complete sentences, including link words such as "and" and "but". Asks "why" and "when".
FIVE YEARS: Speech is easy to understand. Can explain the meanings of simple words.