Diachronic change: early versus late acquisition

There is a long linguistic tradition in which language change is explained in terms of first language acquisition. In this tradition, children are considered to be the agents of language change, or at least the agents of changes in the underlying grammar. Since the early 1980s, this has been formulated in the (generative) terminology in terms of parameters set by children: whereas an older generation acquires one particular setting of a parameter (during childhood), a next generation of L1 children may set a parameter differently, based on the input of their parents, and this may lead to a different output. For obvious reasons this argumentation had to be built on theoretical rather than empirical work on language acquisition. There are no children acquiring Old English or Middle Dutch, and, in fact, the field of acquisition research was until recently much less developed and very often not focused on the type of facts that happened to play a role in discussions of language change.