James and the Giant Peach by Roald Dahl - If I could possibly make up my mind and choose ten of my top favourite books for children, this would be one of them. My favourite character is the Centipede. And you'll see why when you first meet him. I've been collecting quotes for a 365 day calendar, and I found quite a few chuckles in this book. Most of them between the Earthworm and the Centipede.
Johnny Tremain by Esther Forbes - I first read this of my own accord for history. It was so interesting and exciting! It really captured me. I've always really liked these kind of historical fiction, and this was a real winner.
You would not believe how hard it is to find books that begin with the letter J. It's pathetic, as you can probably see. But I think these two make up for it.