So by now Dylan's finished the book and Eleri is on Page 250 (the fastest selling one in history - 2M in 2 dasy was it?). The whole family excpt the two yoinger one have been to see the film -too disturbing for them. Rhodri's appetite for HP is no what it was and I never had any - the books or the films. As for their dangers (as AD raised in a comment) I don't think there are too many dangers for those raised in a Christian home though the possibility of someone being switched on to the occult is at least possible. Isn't Philip Pullman the real bogeyman? In generl my appraoch is to encourage a critical approach, Why do I like this? What's good about it? What's bad?
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.