Your sentence is almost perfect! Here's a corrected version with just a small adjustment for better flow and grammar:
Original sentence:
"Up in the mountains it is cold and windy, the air is thin and food is hard to get. But animals have special ways to stay warm and full."
Corrected sentence:
"Up in the mountains, it is cold and windy, the air is thin, and food is hard to get. But animals have special ways to stay warm and full."
Explanation:
- Added a comma after "mountains" to separate the introductory phrase.
- Added a comma after "thin" to correctly separate the listed conditions.
These small punctuation changes help make the sentence clearer and easier to read, especially for young readers.