My 4-yo, soon to be 5-yo daughter will be officially starting homeschool kindergarten this fall, and I am searching for a good science curriculum for her. She's a very self-motivated learner, and I would be hard-pressed to recall a time that I actually set out with the goal of teaching her something - she asks questions pretty much all day and reads books to her heart's content.

So, given that I also have a 2-yo and a baby due in about a month, I am seeking a curriculum that she can take off with on her own, because of my own schedule, and because of her learning style. She LOVES science, especially biology (she studies the Audubon Guide apps frequently, and has a children's anatomy book that has become a recent favorite), so kindergarten-level is probably not appropriate for her in most curricula. Any suggestions?