Here are the rewritten sentences:

1. Flying a kite in the countryside is very exciting.
⇒ It is **very exciting to fly a kite in the countryside**.

2. Let's go to my uncle's farm at the weekend.
⇒ Amy suggested **going to my uncle's farm at the weekend**.

3. Children are required to wear a uniform when they go to school.
⇒ Children have **to wear a uniform when they go to school**.

4. He spends 20 minutes driving to work.
⇒ It takes **him 20 minutes to drive to work**.

5. My English is more fluent than my sister's. (fluently)
⇒ I speak **more fluently than my sister**.