The original sentence is: "Squirrels hang mushrooms and bury nuts to save their favorite food for winter."
This sentence is grammatically correct. It clearly tells us that squirrels do two things: hang mushrooms and bury nuts, and explains why: to save food for winter.
For a 6-year-old, you might explain it like this: "Squirrels put mushrooms up high and hide nuts underground to keep their food safe when it's cold outside."