Hi Craig,
Good to see you again, too! Did you get a chance to read the articles? It seemed from your response like perhaps you had only skimmed them.
I submit the opposite: Children are supplied with their grammar and language, dictated by the terms and conditions of their cultural environment (read especially parents), and are thus slaves to the thought processes imposed upon them from without, and without their awareness.
That would certainly be more intuitive. But I think the evidence indicates the contrary. This can be seen especially in the case of pidgins (not to be confused with the full-fledged language that is commonly called Pidgin English, from the Solomon Islands), Pidgins are "language salads" that do not contain grammatical constructs necessary for a precision of communication. They are formed when adults speaking many different languages are forced to live or work together. Children born into such language environments actually introduce new grammatical features where none existed before. The resulting language, which does contain a full-fledged grammar, is called a creole.
The most striking example of a language being born from thin air is the arisal in only 30 years of a fully-formed language among deaf children in Nicaragua. In this case, each successive generation of children compacted, stylized, and elaborated the language that they saw their slightly-older peers speaking (signing). It is now expressive enough to enable any type of communication a person might need to do, including descriptions of surreal scenes, poetry, histories, and so on. This indicates that language exists because the human mind is not content with imprecise expression mechanisms: if there are no satisfactory means to express something, a population will invent them.
Another example of grammar being invented out of necessity can be seen in the changes that occurred in English about 600 years ago. A pronunciation change occurred that resulted in significantly less information being conveyed in sound. Since it was no longer possible to discriminate parts of speech based solely on pronunciation, English evolved the unusual feature it has now of requiring a more-or-less set word order. My second link talks about that.
Pinker believes that grammar is invented again and again, generation after generation, by children. If existing constructs are sufficient, the grammar is changed only slightly as it is discovered and assimilated by children. However, if the existing constructs do not enable sufficient levels of precision, children supply new ones, as is seen when languages evolve from pidgins to creoles, often in one or two generations. Thus, the evidence is that if ever we were to raise a population of humans with no language whatsoever and drop them onto an isolated island, they would recover full human language in a few generations.
This is a gloss, but there is really good evidence for this stuff. If you enjoy the recaps on my blog, I think you'd really enjoy Pinker's book.
SNG