In many different contexts I hear a similar cluster of statements around children's 'vocabulary', children's language, children's speech. This runs something like this: many children today have very 'poor' language, very 'little' language, they can't speak properly, they have very poor vocabulary, they can't express themselves...and so on. Or it's more specific than this and it's problem with 'poor' children, 'working class' children, 'immigrant' children and so on.
Most of this evidence seems to come from encounters between the adult who is talking to me and the child or children they are describing. I can say honestly that I've had similar experiences: I've gone into classrooms and tried to engage in a conversation with a child and failed. The child has just spoken to me in very short yes/no type answers.
However, I don't think my encounters with children prove anything at all about how such children speak, how they might speak, or what kind of language they have at their disposal. All it shows me is how that child speaks to an adult, who, in my case, is a stranger, a male, speaks received pronunciation, with standard English dialect elements.
I suggest that if we ever want to find what children can and can't talk like, we need to set up situations in which they are most able to talk fluently, talk in an engaged and thoughtful manner. I would suggest that this would be in situations where they have something to say to each other about something they care about, or something that are deeply engaged in making or doing or planning. This would or should mean having no adult present.
This is not difficult to set up. All it requires is for there to be a job to be done: whether it's planning something that the children really want to do or make; or it's in response to seeing a film or reading a book or poem where the questions that they are discussing are ones that have no right or wrong answer (eg does this book/film/poem remind me of anything that ever happened to me? Does it remind me of any other book, film, TV programme etc that I've seen? Are there any questions I could ask anyone in the book/film/TV programme etc? Can we together answer any of those questions?)
Then all it needs is for the children to agree beforehand for this to be recorded.
Then all it needs is for you or anyone else to be willing to transcribe these conversations and to analyse what is being said and how.
There is a literature to help people do this eg 'Understanding Children Talking' Nancy Martin et al; and even a chapter in my parents' book 'The Language of Primary Schoolchildren'.
I would suggest that we cannot make legitimate statements about children's language unless we start to analyse transcripts of children talking in the situations I've described.
If anyone reading this is interested in carrying out research like this, do get in touch. I'm on twitter, facebook and my email address is on the top right hand corner of my website.