A new school is starting up in New York that will immerse kids as young as 3 years old in a second language. The cost is $40,000 per year, per child. Ouch!! I have 5 grandchildren. Three of them attend French immersion. Another one has French and Latin at school, all public schools.
I also believe that if kids are allowed to read and listen to stories regularly, in another language, they will learn languages, or at least get enough familiarity with them so that when they are older they can learn, if they want to. That is available to all kids, not just those whose parents have lots of money to waste.