Good questions, everyone! I will try to answer them. 
Will this be too light for my 3rd grader?
While Outdoor Secrets is recommended for 1st and 2nd graders, that is only a recommendation. Because every child is different, it will depend on the abilities of your 3rd grader whether it will be too light or not. Have you looked at the sample yet? That will give you a good idea of what the book contains. You should be able to get a good feel for if it is too light for your 3rd grader.
I am assuming this would be a typical school year worth of science?
There are a total of 50 lessons. You get to decide how many lessons you do each week. If you did two lessons each week, it would be about a year’s worth of science. Oh, and feel free to not do the book in order. If there are lessons that would work better in warmer weather and it’s the middle of winter, by all means, save those lessons until it is warmer.
Having read your latest post about using living books/nature study to teach science, I am still wondering at what age you recommend more formal science study?
Personally, I recommend that more formal science studies begin around 7th-9th grade, depending on how much you have done with nature study and living books. When I say formal science I mean subjects like general science, physical science, biology, chemistry, and physics. Charlotte Mason actually used textbooks alongside nature study and living books for formal science studies. Of course, this was after building a good foundation with living books and nature study in the earlier years.
I realize that many moms wonder if nature study and living books are enough. Let me reassure you that they are! In fact, many children with that good foundation will fly through general science or can skip it altogether.
Is this the new science curriculum you were working on, or is there another one coming out as well?
Yes, this is the first of what we hope to be several science companion books.
