Chomsky

Children have an innate ability to learn language due to a language aquisition device (LAD) in their brain. This allows them to know the universals of language and therefore they can learn any language from birth. 

Evidence for: - Berko's wug experiment, stages of grammatical development, virtuous errors, overextensions, Brown's U-shaped regression model, babbling (deaf children) children use imaginative language. 

Evidence against: - Didn't acknowledge the importance of interaction, deaf children do not learn to speak, Genie (children might have a LAD but past a certain point (criticle period hypothesis) it is not triggered, LAD has never been found.

Summary - Chomsky explains how children aquire grammar but does not recognise the importance of interaction and input.