speaking, there are many benefits to encouraging multilingualism in people from the earliest ages. It's good for the brain, good for further education, may fight off dementia in old age, and just might allow more people to see each other's point of view in ways that can affect the social and political. http://science.sciencemag.org/content/330/6002/332 I wonder what everyone's first three choices would be beyond a child's first language given the state of the world today?
For an American in 2019, it seems Spanish, Mandarin, and perhaps German or Arabic would be practical choices.
Many families that have other languages as a native tongue, quite often speak them at home. My Nephew can carry a conversation in Tagalog, my best friend from childhood can speak both Polish and Russian fluently. Both from just having the languages spoken around them growing up. I understand more than I can speak in Spanish and Italian, bits and pieces of Hungarian, Greek and Polish.
Unfortunately, while having the enriched input of native speakers around during the Critical Period can be a strong foundation, it is not enough to actually achieve full bilingualism. This is how so many second or third generations lose their heritage languages.
