bein_hasdorim: Regarding those who didn’t work on Shabbos in the early 1900’s, for the most part, it wasn’t ingrained in their children. In fact, most of the children did not stay frum.
R’ Moshe Feinstein said about this that the problem was, while the parents were moser nefesh to keep Shabbos, they kept saying S’iz shver tsu zayn a Yid – it’s difficult to be a Jew. Their children heard them say this, and wanted no part in it when they got older.