As a kid, you know you aren't perfect, and when you've done something to offend your parents, it can be hard to know where to start to say "I'm sorry." While you can say it in person, perhaps you don't feel as though you will get out everything you want to say that way. A good alternative is to write an "I'm Sorry" letter to your mum and dad, that explains why you did what you did, why you are sorry for doing it and what you've learnt.
State the offence to start the letter. This reiterates that you know exactly what it is that you did wrong. For example, you might say: "Dear Mum and Dad, I am writing this letter to tell you I am sorry for coming in past curfew last night. I was supposed to be home by 11 p.m. and instead, I ended up coming home at 1 a.m."
Write a paragraph detailing why what you did was wrong. It might say "I know it was wrong to come in late because you've already extended me the courtesy of allowing me to stay out later than you originally wanted. I broke your rules and disrespected your home by coming in so much later. Furthermore, as a young person, being out so late is dangerous because something bad could have happened to me."
State a formal apology. This is the crux of the letter and should be genuine and heartfelt. It might read "I am very sorry to have disobeyed you and broken your rules. Moreover, I apologise for making you worry about me."
Offer a corrective action. This shows responsibility on your part and shows your parents that you are genuine in your feelings of remorse. You might say, "For the next few weeks, I will come home an hour earlier than the time we set, and I will keep your mobile (cell) phone ringer volume up at all times should you need to reach me when I am out with friends. Moreover, I will set an alarm on my phone for 20 minutes before my curfew to remind me to stop whatever I am doing and head home."
Close the letter with a final apology to your parents. You might try "Again, I am very sorry mum and dad, and I will do everything in my power to ensure nothing like this ever happens again. I love you and I appreciate everything you do for me."