IMO, yours are a little young; even to fully appreciate the stories, whether the ‘mother nature’ thing was there or not. I think after age 6, not only will they be able to more readily separate the fictional literary term of ‘mother nature’, but also be able to understand the living lessons within the storyline that TB put in there to learn about creation. Does that make sense?
I think at their ages, it is prime time to impart to them the Creator’s handiwork explicitly, through the Bible stories and books that don’t use those literary terms. Also, the time to instill into them the surety of the Creator and love for His creation.
We live in such a pagan society now; speciafically an earth worshipping pagan society (my sister is a pagan, so I have always been vigilant in this area); it’s imperative to get that surety in there early. Then later, they won’t have any discernment issues.
Personally, I would shelve it until the youngest is 6 or 7. Here are some great books for their ages that mine enjoyed from Rod and Staff:
God is Good Series (my children loved these)
My Little Farm Book
My Little WIld Animal Book
G-d’s World and Johnny
Dictionary of Bible Animals
Caterpillar Green
We Want to Learn about Zoo ANimals
The Locust Story
3-G-d’s Miracle books
Nature poetry-here and here
Creation-based coloring books
You could read the Christian LIberty Nature Reader K out loud-http://www.amazon.com/Christian-Liberty-Nature-Reader-Book/dp/1932971130
LAstly, are the books from AIG and MAsterbooks suitable for their ageshttp://www.answersingenesis.org/PublicStore/catalog/24-Years-Old,183.aspx
Buddy Davis books aloud; like the Marvels of Creation 3-book series and he also has some DVD’s.
With this foundation, combined with actaul nature observation nature study, there will be no doubt that they will enjoy the BUrgess books and there will be no discernment issues.
HTH, Rachel