I agree. When I moved to I of Arran, my eldest were six and almost five. Within a week of starting school they were speaking with Scottish accents. Not quite the same as learning a language but similar. Now, 18 years after leaving Scotland, they still have a hint of the accent left and people tend to think they are Scottish.
Interestingly, my youngest was nine months when we went there and has never had a Scottish accent. His is London, like mine.