Wasn't there a HN post recently arguing about the lack of difference between adults and children learning languages?

I believe so, a large crux of the argument was that true immersion learning becomes much more difficult if not impossible as an adult because while children will just speak to other children normally, an adult will “tone it down” and talk to someone struggling with a new language, ultimately putting the adult at a disadvantage, since the adult might not hear as much natural language in the new tongue.

Just having the social, familial, and cultural freedom and encouragement to practice abstract thought would be an important first step, otherwise the teaching isn’t very effective.