Here are the identified mistakes and their corrections:

1. **Mistake:** are
**Correction:** is
**Corrected Sentence:** Having leisure activities is truly important to the elderly.

2. **Mistake:** staying
**Correction:** to stay
**Corrected Sentence:** Although she wanted to go to the museum, she decided to stay at home.

3. **Mistake:** spending
**Correction:** to spend
**Corrected Sentence:** Parents are concerned that their kids may be to spend too much time on screens.

4. **Mistake:** is
**Correction:** can be
**Corrected Sentence:** Collecting coins can be exciting, but it can also be relaxed.

5. **Mistake:** sound
**Correction:** sounds
**Corrected Sentence:** Cloud watching sounds weird, but Hang adores it.

6. **Mistake:** in front
**Correction:** in front of
**Corrected Sentence:** For some young people, enjoyment involves sitting in front of a computer.

7. **Mistake:** on
**Correction:** about
**Corrected Sentence:** His parents are thinking of banning him about using the computer.

8. **Mistake:** carefully
**Correction:** careful
**Corrected Sentence:** When you play games online, be careful when making friends with strangers.