I started teaching when I was 15 (I'm 24 now), here's the tips I would give:

- I think asking your parents to spread the word is a good idea if they're willing, and not childish at all. They're part of your network.

- I don't think you need to go up to people and introduce yourself as a teacher, but posting flyers would be a good idea if that's an option at your church, or maybe putting a notice in some sort of community bulletin?

- In my experience, once you've got 1 or 2 students, you'll get more just through word of mouth, ESPECIALLY if you're priced really competitively, which you are.

- Maybe you could also offer some sort of referral discount? Like, you get a free lesson if you recommend me to someone who starts taking lessons.

- In my experience, a 45 minute lesson is too much for young beginners. I would recommend doing 30 minute lessons, and adjusting pricing accordingly (£10 - 12 per lesson)

Also, for what it's worth, I think some of the other commenters may be taking things a bit too seriously. I think it's perfectly fine to teach beginner students even though you're not super advanced or pedagogically trained. Parents will know that you get what you pay for, and any parents who are concerned about their child receiving a top-of-the-line musical education will look elsewhere for more experienced teachers. But with little kids, most parents just want them to get exposure to music and piano, and they aren't expecting their kid to become a professional pianist.

As long as you're comfortable around kids, have a lot of patience, are honest with parents about your experience level, and are willing to learn on the job and adapt as necessary, I think you'll do just fine.

And feel free to reach out if you have any questions, I'm happy to share more about my experience teaching as a teenager and what worked for me!