I did Apologia Land Animals when my dd wa 9/10 and I kinda wish I had waited and done it later. They are so rich in vocabulary and in depth stuff, but they are certainly textbooks, even though beautiful ones:) The Nature Study series covers much of the same information in a much gentler, more integrated way, and they are a fantastic intro into the world of plants, animals, birds, etc. I like what bookworm ( I think it was you) said in another post about the tendency to ‘feminize nature studies’- its true but we don’t have to do that. The boys can classify rocks, get grubby looking for worms, seashells, etc, climb trees for leaves- so much. The Apologia book didn’t leave us much time or space for ‘getting out there’ if you kwim? The book took a lot of time, and we did the lapbook pages with it so it was hands on but it still took a lot of time I think would have been better spent learning how to observe, classify, really touch feel and see things- then move into the books. Just my opinion but if your kids are under 10-11 I would wait- there is lots of time for the books later on!