When talking about literary criticism, Deleuze says that we must avoid bringing pre-fabricated categories to the text, but instead generate new concepts from the text. We listen and allow the text to destroy the existing categories of analysis, which were in any case fashioned for older texts.
Now, I wonder if there are philosophers and writers who, rather than simply writing about children, have generated new methods and new concepts from children and from childhood.
Lewis Carroll is an obvious example, but so too I think is James Joyce. My 4-year old recently called me a "scubious potman". He couldn't (or wouldn't) tell me the 'meaning' of this glorious phrase, but of course it was a word made for and from its connotations and effects. Children's relation to language, to the molten potential that precedes our utterances, the quick invention of lexical monsters, is something that to me informs the writing of Finnegan's Wake more than does the idiom of dreams.
In terms of philosophers, Deleuze is the name that comes to mind. Some of Deleuze's concepts are coinages learnt from the observations of babies. His re-thinking of the notion of the 'Subject', for example. A small baby is not a 'subject'. Extreme 'upset' can be seamlessly followed by a smile and a chuckle - the 'trauma' has not been registered as it would be by an adult. Each affect is only a kind of simulacrum that plays on the surface or traverses the features. With an adult the upset lodges stubbornly, accrues a 'meaning, sinks into the texture of memory - cannot simply be superseded. In other words, the adult has depths whereas for the baby there is only a succession of 'emotions' - joy, surprise, distress that play on the (sur)face and then vanish. These are the disembodied and decontextualised affects that recur in Deleuze's thinking, in his reflections on cinema, for example, and the ability of the close up to wrest and affect from the subject who 'expresses' it.
Anyway, these are a just a couple of stray and incomplete observations. Comments most welcome..