The author is married to a minister, so there is a spiritual aspect. Their deity is "Heart", who loves them, gives them trials, and even at some point in the past, sacrificed for the animals. There is a mist surrounding their island that protects them (and also doesn't allow anyone back in by way of the sea if they leave) that seems to have a hint of spirituality. There is mention of evil, and a dungeon full of horror and palpable evil that speaks to a character. There is a priest, but he seems less of a Hindu-type priest and more of a Church of England-type priest. He speaks blessings over people, reminding me of Isaac blessing Jacob and Esau. The only thing I didn't really feel good about was when he blessed the evil dungeon with candles and light, to drive out the darkness, but even that wasn't like dark magic.
There is a bit of drinking wine (the usurpers try to make the king look incompetent), knife murders, and implications of poison murders. Also, the bad guy institutes a new law--culling--that is slightly disturbing. All in all, they serve to paint a brilliant picture of the setting (I think).
I would recommend this series to middle school kids, or elementary if they are well-grounded in the Bible. Nothing (in book one, at least) that would cause someone to become an atheist, but it is spirituality not directly from the Bible, so there's that.
Have you read this series? What did you think of it? Would you recommend it for kids?