Corrected sentence (simple): Airplanes fly far and very high to avoid bad weather and busy times.
Another natural version: Airplanes fly long distances at very high heights to avoid bad weather.
Why this is better (easy words):
- We keep "Airplanes fly" because that is correct.
- We add "and" or say "very high" so it sounds clear: "far and very high."
- We use "to avoid" instead of "avoiding" so it clearly tells why they fly high (they want to stay away from bad weather).
- "Rush hours" is about cars on the road. Saying "busy times" is simpler for a child. If you meant roads, say "rush-hour traffic."
If you want it even shorter: "Airplanes fly very high to stay above bad weather."