Arthur C. Brooks argues that children absorb values like gratitude and faith by watching what parents do, not what they say. If you complain constantly, your kids will too. Model the behavior you want to see.
Chapters
People ask me all the time, what do I do to keep my kids in the faith? All that matters is what you do. It really doesn't matter what you say because that's what they will model. That's what they see. This is the wiring is established. So if you want your kids to be more grateful, be more grateful. If you want your kids to be less ungrateful about the beautiful life that they have, be less ungrateful. Don't see them have you grousing and complaining and just being kind of grumpy all the time. One of the ways that you do that is by talking to them at dinner about the things that you're grateful for. And if you want to raise them in the faith, then practice the faith assiduously, seriously, with your heart, with your whole heart. That's how you do it.