What is “frum” oomis? It’s just a Yiddish word that has developed into some sort of popular term– for what, exactly??
If we are discussing Halacha, a married woman must cover her hair. However, as morahm pointed out, there are a lot of other mitzvos out there. Grandparents, or anyone we love and are close with, may be in violation of any or many of them. How to explain this to our children can be tricky, but may be necessary. Waiting until they ask is not always advisable as in the case of, shall we say, blatant disregard of Hilchos Shabbos, or Kashrus. The best place to start is by showing that we love and respect the relatives in question. We also love our Creator, and His Torah, which we accept as an extraordinary gift and privilege. We can express the fact, in an age appropriate, nonjudgmental, way, that some people may not have been as privileged as us in opportunities for studying Torah, and that we ourselves continuously try to improve our knowledge and observance (Tatti leaves early / comes home late every day, because… etc).