I teach Sunday School for 7th and 8th grade. (I'm also single, so I haven't raised kids myself.) I've talked to a few parents about what they do. Now maybe it's because we're a moderately liberal church, but I find that parents don't talk with their kids about their own devotional life. How are they going to take me seriously as a teacher when I try to get them to do something that nobody they know does? The thing is, I know many of these parents actually do pray and read Scripture. Somehow it just never occurred to them to talk with their kids about their own private lives.
I also asked about praying with their kids. I got two answers: "pray?" and implications that they were saying "now I lay me down to sleep" kind of things, i.e. prayers for 5 year olds.
I guess what I'm saying is that for teens I think things change, but I think it's still important to talk about it. I'd be happy to see parents doing some devotionals with their kids, but at some point they need to start developing habits of their own, which might continue when they're living on their own. So I'd talk about your faith, talk about this week's sermon, what the learned in Sunday School, and also what they're reading, how they're praying, etc. If you do devotionals as a family, that's great. (My parents didn't, because of bad experiences with it when they were younger.) But in terms of their private devotional life I'd prefer to see you guide them into doing it themselves, and only sit with them sometimes. One thing you might do is suggest topics for prayer, e.g. if you know something has happened in their school. You might ask whether they have in prayer concerns, so you could include it in your prayers. You might ask them to join in some of your concerns.
Of course this assumes that they're committed Christians. That can't be taken for granted, obviously.
