at learning several languages at once. Raising a child bi-or multi-lingual is exceptionally easy if the kid is being exposed to native speakers, preferably on a daily basis.

Even as late as 5 or 6, typical start of formal schooling, the vast majority of children will learn multiple new languages very easily. Depending on when you first learned a foreign language, you may think it is always that difficult. Not for little kids.

Why do you think it is so many Europeans speak multiple languages, mostly with a high degree of fluency?