Surprisingly, for most of the book it was slow going. In the first two sections I didn't find myself caring about any of the characters or even compelled to pick the book up beyond trying to get it over with so I could move on to something else. I didn't really become interested until page 337 (painfully close to the book's conclusion on page 399) when Lyra cleverly tricked Iofur in a way that hadn't even crossed my mind. From there until the end there was plenty of suspense to sustain my interest.
Because of the way most of the story dragged for me, I can't imagine a child sticking with this book (although I am sure there are many that must have). Not only that, but even I didn't see that anyone was trying to "kill God" like I'd heard. (Or will that come in one of the other two books of the trilogy?) One of the main characters was trying to destroy death, but no one said anything about killing God. Even if the author intended this story to be about killing God and somehow masked that idea with some sort of symbolism, I didn't pick up on it, and surely a child wouldn't either. For those two reasons, I have no fear of allowing my own children to read the story, although I won't push it on them any more than I would suggest any other book I didn't especially enjoy. My opinion is that this book is indeed as harmless as Harry Potter. (And, in case you were wondering, my opinion is that reading Harry Potter books won't make your child interested in practicing witchcraft any more than playing cops and robbers will make him grow up to be a burglar).
I haven't seen the movie (although I plan to), but I can totally picture Nicole Kidman in the role of the kidnapping lady, Mrs. Coulter. (Is this her role? It must be, as there is really no other significant adult female role.) Yet again, I can imagine the movie might be better than this book, but I guess I will have to watch it and see.