(My answer to this question at Quora.com)
Yiddish is being passed down to the younger generation only among the Ashkenasi ultra-Orthodox Jews (in Israel and in the U.S.—mainly Brooklyn). They do so because they consider Hebrew a sacred language to be used only for the study of Scripture, and not for the profane needs of everyday life.
Everywhere else Yiddish has pretty much died out.
The Ladino-speaking Sephardis are mainly the Jews of Greece, Turkey, and pre-independence Israel. None of these formed closed communities like the ultra-Orthodox Ashkenasis in Israel, but assimilated in the general Israeli environment, and generally accepted the (misguided) local dictum in Israel in the 1940s and ‘50s that the patriotic thing to do is to speak to their children in Hebrew, rather than Ladino.
My wife’s parents (who are from Turkey) are a case in point: they spoke Ladino with each other, but did not pass it on to her or to her brother and sister—something that they all now regret.