i know of some bi/multilingual families in the us who’d talk to each other in their native tongue when they didn’t want the kids to know what they were saying.
i speak my dad’s native spanish as well as dad’s learned portuguese, but i don’t speak the polish or norwegian from the other side of mom’s family. (she’s also latina but doesn’t natively speak spanish)
however, i’m learning the two i don’t know, and practicing polish (the language my mom does know) with her
I had a couple friends who were raised to only speak English at home because their parents wanted them to be fluent and native sounding. One of them, the parents only ever learned basic English so as a concequence it is difficult to communicate any complexity. And functionally no communication with extended family.
That’s a very old fashioned viewpoint and now we know extra languages dont ultimately prevent acquisition, although it can slow thing down a bit at first for an individual language.
I think knowing other languages at any level is only a good thing and kids can learn so much easier.