I’ve seen a number of children go through the same process, and I’m asking this question because I’d love to understand them better.

Children, after relocating to a country with a language with which they are entirely unfamiliar, will often acquire a near-native accent, while adults rarely do. I ask about accents in particular as language acquisition is a very broad subject, and I’d like to focus the question on only the differences between adoption of near-native accents in adults, and the adoption of the same in children.

If critical window theory is to be believed, most of the commonly-accepted windows have been passed by 3-5 years of age. Despite this, there continues to be a significant difference from adults in the rate of near-native accept adoption, and in the average level of language adoption, well into the early teens if not later. What would account for this inverse relationship between age and near-native accent adoption?