Both sentences are pretty good! Here are two easy, corrected versions you can use:
1. A kiang is a wild donkey that lives in the mountains and sometimes skips along the cliff tops.
2. A kiang is a wild donkey that bounces along the cliff tops like it’s playing hopscotch!
Why these are a little better (short and simple):
- Simple words: 'sometimes' is easier to understand than 'casually.'
- Clear place words: 'along the cliff tops' sounds clearer than 'on cliffs.'
- Playful phrase: 'like it’s playing hopscotch' is fun and easy to picture for kids.
- Capitalization: Starting the sentence with 'A' is correct.
Pick the first sentence if you want a simple fact. Pick the second if you want a playful picture.