[…] there is evidence that second language learning parallels first language learning in striking ways, at least on the syntactic level. Children already in near-adult command of native language A, that is, with a well developed grammar, will treat a second language B like a first, making hypotheses about it that lead to development of output closely remembering that of the first language learners of Language B […].
- Traugott (1977), a pag.83

The main difference between first and second language learning seems to be the speed at which developmental stages are reached–second language learning is considerably faster, but we find the same reliance on word-order to mark possessive, subject-verb-object, etc., the same lack of functions, and the same sorts of over-generalizations.
- Traugott (1977), a pag.83-84