Just the right size

I'm a person who has a great deal of trouble with scientific concepts. This book explained some principle in science, I think, and I believe I understand the principle better after reading this book, though I couldn't tell you the name of the principle and I doubt if I could explain it very well. It has something to do with why animals cannot be enormous in size and it has something to do with volume and doubling height causing a big jump in volume. (Glad I am not being tested on the material in this book as I quite obviously am barely grasping any of this.)
The pictures are funny and helped me understand this concept better. If I really wanted to understand this concept, this book would be just the one to read, I think.
A bit:
“Here is a Little Thing. It could be anything—a car, a log, a bar of soap—but it just happens to be a creature (even if it looks a bit like a cube)....
Now let's meet Big Thing. Big Thing is TWICE the size of Little Thing....
How many Little Things would it take to make one Big Thing?
If you look carefully, you can see that Big Thing's surface area and cross section are FOUR times bigger than Little Thing's. But Big Thing's volume and weight are EIGHT times bigger.”
Children's reactions:
The group of eight first graders who looked at this book had very little interest in this book. Perhaps this book is aiming at an older audience.