Grammar help for a 6-year-old — Correcting: The desert sand gets very hot in the day. Many animals hop so their feet don’t burn.

Original: The desert sand gets very hot in the day. Many animals hop so their feet don't burn.

Two simple corrections:

1) The desert sand gets very hot during the day. Many animals hop so their feet don't burn.

2) The desert sand gets very hot during the day, so many animals hop to keep their feet from burning.

1. Change "in the day" to "during the day": "During the day" sounds more natural when we talk about daytime.
2. Make the reason clearer: Instead of "so their feet don't burn," you can say "to keep their feet from burning." Both are correct, but the second is a little clearer about why they hop.
3. Contractions: "don't" is fine to use when talking to children. For formal writing you could use "do not."
4. Punctuation and capitalization: Your sentences already have correct periods and capital letters.

Short version to use with kids: The desert sand gets very hot during the day, so many animals hop to keep their feet from burning.