It took my older son a little longer to realize he should pay for half of our restaurant meals, than the younger one. We gave little hints. It's been a few years since he started doing this, and now, of course, DH will often say he is treating. It's just the idea of it. Sometimes, on holidays, I have to ask them to bring something, but I also do that with my friends who are coming. DIL many times has spent Amex gift cards from her employer on meals or presents for us. I don't know my other DIL as well, since they live in CA, but she follows my son's lead. She has always been gracious and helpful when they have stayed here, and I appreciate it. I hated my mother in law, but then DH had horrible, abusive parents, who subscribed to the "do as I say, not as I do" theory. I swore not to be like that, and just keep my mouth shut. I always say the proof that my kids are OK is in the way they treat their wives. Never wanted any woman to say, "What the hell did your mother do???"
And yes, better parenting is the key. It's just that many people have no good role model for that.