My family is not frum, and my grandfather gives out money to all the grandchildren at our seder. I refused the money, but my father took it and put it in my room. Can I use this money?
Seems like it should be no worse than the case where a Jew deliberately violates Shabbos by cooking food, where someone else is allowed to eat that food as soon as Shabbos ends (Shulchan Aruch, Orach Chaim 307:1).
[Taz (:1) and Shach (:2) say that the reason why in this case we don't require waiting after Shabbos for the time it takes for the melachah to be performed (as is true if a non-Jew did it, whether you instructed him to do so or not - ibid. 307:20 and 515:1) is because if you tell a Jew to do a melachah, he won't listen. So it is possible that a Jew who is not (as of yet) Shabbos-observant would be in the same category as a non-Jew for this purpose; even if so, though, then the latter rule would apply - the object does become permitted following a (short) delay after Shabbos ends.]
(CYLOR, of course.)