I know that this was asked awhile ago as well. . .but I have a few suggestions for you depending on your philosophy of education. . .
I really like Janice Van Cleave. Search for her books at the library and you're bound to come up with lots of titles. She does mostly experiments in her books and then explains why or how they work.
I also really like Usborne, & Eyewitness books.
Here are the problems with those: they are not a curriculum as much as information, and reading. If you're okay teaching that way, that's where I would start.
However, some people want the whole "tell me exactly what to do" type thing (and of course that's fine too

! If you're one of those I would look into McGraw-Hill publishing. They write very thorough text books and I have liked them very much.