Full Idea
Ninety percent of most young children's utterances are grammatical.
Gist of Idea
Children speak 90% good grammar
Source
Georges Rey (Contemporary Philosophy of Mind [1997], 4.2.4)
Book Reference
Rey,Georges: 'Contemporary Philosophy of Mind' [Blackwell 1997], p.119
A Reaction
This is good evidence for some sort of innate element in the grammar of language. But the accurate grammar is not in a particular language. Good communication must be the driving force in all this.