Charmed Life by Diana Wynne Jones 1998
One of the Chrestomanci novels, which predate the Harry Potter books, and are gaining popularity as people look for more kids' wizardry books to read. Cat and Gwendolyn are taken from their foster home to the leading magician's castle, since they show magical promise. There are science-fiction elements, and a surprising betrayal. A lot less goes on than in the Rowling books, and it is less funny. Your kids might like it, though, as it gets uniform raves on Amazon.
Beyond the Deepwoods by Paul Stewart and Chris Riddell 1998
Twig is brought up by woodtrolls in the Deepwoods, but isn't one of them. He goes off on a quest, and meets loads of creepy or kind (or both) Deepwoods denizens, most of whom are illustrated very well on nearly every other page. There is a map, typical of fantasy books. The world is hanging in space, and some rocks are lighter than air, and used by the sky pirates for their ships. The episodes are fun -- Patricia likes this book, too. Twig finds out that his dad is the top sky pirate. Of course there are sequels. The worst monster has a great name - The Gloamgozer.
The Snow Spider by Jenny Nimmo
A very slim volume, with a slim tale of a boy in Wales, who is a once-in-seven-generations wizard, and of his missing sister, who may have returned from an icy, magical world. Not bad. Probably a good read for a child (Ross' review was a grunt). When I first found books on the internet, I tracked down Shadow Castle, a book about fairies and true love that I read a couple of times when I was very young, and which really transported me to another world, so that I came back to the real one with a thud and a heavy feeling. But when I reread it as an adult, there was not much there. By contrast, Island of the Blue Dolphins is still a good read, and Ross read it twice.
Two of these books involve dead or missing parents. P says she heard Rowling in an interview say that you really have to get rid of the parents before children can start having anything interesting happen to them!