In a somewhat hand-wringing piece, CNN reports on the lagging Christianity of American teenagers:
"Though three out of four American teenagers claim to be Christian, fewer than half practice their faith, only half deem it important, and most can't talk coherently about their beliefs, the study found."
I am intrigued here by this thought of someone who "can't talk coherently about their beliefs." (This is an idea that also finds life in evangelical Christian apologists who preach the importance of "knowing what you believe" to Christians--ignoring the fact that not knowing what you believe is, in the first place, pretty good evidence that you don't believe it.) I would think that one of the markers of a person's beliefs is that, generally speaking, they can talk about it, so that an inability to make sense of or talk coherently about some p pretty much means that you don't believe p.
Probably the kids just don't care very much about religion, and "Christian" is just the easy default answer to the religious question for more or less cultural and historical reasons. The label has no deep meaning for most kids. And that is surely nothing much to worry about (pace the not-very-objective researcher interviewed for the piece), unless you have some advance idea of what people should, in any case, believe.