It's rather rare really. The truth is that most 2nd generation Americans are strictly English speakers because first generation American parents tend to only speak English to their own children, even if they are fluent in their family's tongue. That seems to be especially true for Italian Americans, even the children of parents who came here from Italy as teenagers are rarely fluent in Italian.

I've never even heard an Italian American mobster on wiretap speaking Italian to anyone, only a few curse words or exclamations here and there.