Final answer:
According to Chomsky, the ability of children to rapidly and spontaneously acquire language, including the ability to apply grammatical rules and make characteristic errors like overgeneralization, undermines a behavioral account of language learning and supports the concept of an innate language acquisition device.
Step-by-step explanation:
According to Chomsky, one observation of language in children that challenges a behavioral account is the spontaneous and rapid acquisition of language without explicit reinforcement or formal instruction. This phenomenon is evidenced by children's ability to understand and apply grammatical rules in novel contexts, even making errors such as overgeneralization that suggest an inherent grasp of language rules, rather than rote learning from feedback. Such observations led Chomsky to propose the existence of a biological mechanism for language acquisition, which he termed the Language Acquisition Device (LAD). This concept highlights the innate capability of children to learn languages and formulates an argument against the behaviorist perspective, which posits that language learning is solely the result of reinforcement from the environment.
Children begin to develop their language skills from a very early age, without the need for formal training, which contrasts sharply with the difficulty adults experience when trying to learn a new language. The ease with which children acquire language suggest that there is a critical period for language learning which diminishes as individuals age. Furthermore, children from different cultural backgrounds and languages seem to follow a similar pattern in language development, supporting the notion of an innate predisposition to language learning. The richness and complexity of linguistic development in children provide a strong argument against a behaviorist account of language acquisition.