The Golden Compass

Since His Dark Materials is the anti-Chronicles of Narnia, it makes sense that you should read The Chronicles of Narnia . C.S. Lewis' masterpiece Narnia is a classic of the genre. While it's very clearly a Christian allegory, it can be enjoyed without reading too deep into the Christian subtext. The writing is great and it's a great magical adventure for both kids and adults. 

I also suggest reading Garth Nix's The Abhorsen Trilogy . Garth Nix is a fabulous writer and Abhorson is a chilling horror fantasy that really sucks you in. It's YA (young adult) but don't let that stop you! Garth Nix's newest series,Keys to the Kingdom , is also a great read, both for the kiddies and adults, one of the better series for kids. 

Don't forget to read Jonathan Stroud's very impressive The Bartimaeus Trilogy It's an action packed thrill ride about a magician's apprentice who manages to summon a powerful genie (Bartimaeus). Bartimaeus is less then pleased with this turn of events and tries to sabotage his young master at every opportunity. Hilariously funny, at times very dark, with great writing, a great cast of well-developed characters, and an interesting world, Bartimaeus is a must read series (for both kids and adults). 

And finally, Harry Potter. I won't bother explaining why. You might note that each of these YA books can be read by children, but at the same time they are equally entertaining for adults. And every one of the books mentioned starts of pretty lighthearted but becomes quite dark in tone and content. While this may not be great for 6 year old Johnny who is wondering why his hero dies a horrible death, it makes for a more sophisticated plot. The sweet is not as sweet without having the bitter.

 If you are specifically looking for books your kid might like, i suggest you visit The Top 10 Fantasy Books for Kids list.