Often, children in bilingual homes learn their parents’ and grandparents’ language to a functional but abbreviated degree. They can converse fluently on a basic level, but never master the level of language required to discuss complex topics and miss many of the pickier aspects of the language’s grammar. Linguists call this “heritage language.” People who speak a language only at this level seldom pass it on to their children, even if they happen to marry someone who also speaks the language on the same level.
Extended family members are often dismayed to see that their kids only reach this level in their home language, if even that. Spanish and Chinese speakers have it somewhat easier because of how much media is available in their languages. Also, they can live in neighborhoods where a critical mass of people speak the language, signs are written in it for blocks on end, etc. For speakers of Polish, Hebrew, or Tagalog, however, this is much less likely. The truth is that if kids raised in America are going to grow up speaking home languages like those beyond the “heritage” level, in most cases they will have to spend holidays and every summer in the country where that language is spoken, unless they are to lead lives of unusual isolation within the larger society, which preserves languages like Yiddish (hardly dying as it is often claimed, given that about 150,000 people are using it at home in the United States as I write) and Pennsylvania Dutch.
Note, however, that conditions under the virus have created something ominously close to just that kind of isolation for the time being. Children whose Bengali or Danish was slipping have now been spending infinitely more time with parents (and especially in immigrant communities, grandparents) and have been able to use the home language all day every day for the first time since toddlerhood. I have heard from many parents who say that they are pleased to see their children’s skills in the home language explode or at least improve. A summer immersed in a language can do wonders, as veterans of Middlebury College’s famous language-learning program can attest. The lockdown is clearly going to amount to the equivalent of about two summers, and there are mini-Middleburys happening in millions of houses worldwide.