I've done something irreparable.

Maybe that kid actually already held the key from the bench and made fun of you?
If not, someone picked up the key and it was probably delivered to the police box where the lost item was stored. It may take some time for it to arrive at the police station.
Either way, you tried to return it, so it's not bad.
Let's stick to the attitude that even though they tried to return it, they made fun of me and didn't accept it.
Also, it's very important to properly write the series of steps in a sentence like this!
So, once again, please write that flow on paper and write the circumstances and processes leading up to “this happened” in addition to you guys.
Otherwise, people will think that loud people, people with bad intentions, people who are good at lying, and people who only try to protect themselves are right; there are such places of misconduct in the world, so please dodge them well and deal with them well so that you don't get in the wrong position.
If they ask for something, you can get involved and tell the truth for the first time there.

Just yesterday, Osho-san was playing with 3 children, and only 1 child was left behind, and the other 2 made fun of that child and tried to make them run ahead and chase him. Scenes like this are common. It's still been a few years or ten years since I first jumped out into this world when I was a kid. That's why they say they're desperate to find a safe zone for themselves. That's why they sometimes make fun of other people and try to “gain an advantage (get the position that you're stronger, you're better).” That's why they make fun of quiet kids. Even in Totoro, there's a line called “Hey, you guys, haunted house!” Also, I want them to take care of this, and I want to be in a position where I have a stronger advantage. It's probably the mentality of wanting to control the other person.

The key is one that has a spare key. Even if you lose it, it's easy to have the key removed at a bicycle shop. At most, it's a few thousand yen. But it's not your fault. Even if I was that child's parent, they said, “My kid is bad. I'm so sorry.” This attitude is a sincere parent's response. I think that child is also reporting that only you are the one to blame, so let's properly write the circumstances and flow of losing the key, including this page, using AI etc. to competently “summarize this story in a short way so that other people can understand it.”

I was so anxious and scared. Your sincere heart, which is deeply remorseful and troubled that you have done something irreparable, is fully conveyed from the sentences.

Buddhism believes that no one is perfect and that we learn from our mistakes. They didn't intentionally hurt people or steal things with malicious intent. This is by no means “irrevocable,” so please calm your mind by taking a big, deep breath first.

Realistically speaking, if you ask a bicycle shop for a bicycle key, you can exchange it for a new one for around two to three thousand yen. Don't worry, you will never be charged a large amount of money. Also, one of the reasons was that my friend playfully ran away this time. You don't have to take all the responsibility alone, and it's a problem that can be fully solved by reflecting on each other and paying half of your pocket money at a time.

I understand the fear of being scolded by your parents and not being able to go out to play, but hiding things will later become heavy baggage for your heart. Please gather your courage and speak honestly as you are. Parents are always on their side to help solve the problem.

If you can honestly apologize to your friends and say “I'm sorry for that time,” you'll be able to make peace right away. Don't hold it alone, and first have the courage to rely on an adult close to you. I hope the fog in your heart clears up soon.

Worship
Engiji Temple Shakujo

I read it.
There was such a thing, wasn't it? You must have been very shocked and hurt. I don't know the details, but I understand your feelings from the bottom of my heart.
First, let's calm down and thoroughly talk to your parents about the circumstances up until now. Please also explain your situation and feelings clearly. I'm sure your parents will understand you too.
Also, please calm down and explain the circumstances to the other person's parents.
I think you were playfully bullied or harassed by that friend. Let's not talk about it thoroughly so they can understand it either.
I think your parents and other parents will probably understand you.
Please don't worry.
I sincerely pray that your parents will understand you and that you can live every day with peace of mind, and that you can live well with your friends without being messed around or harassed. We wholeheartedly agree

I think that's my friend's fault too. There is a risk of easily lending things from your house to someone. Also, borrowers must take responsibility until they return it.

This time, I think both the friend who lent it and you who borrowed it were acts that they thought would be good from their daily relationship, but due to the friend's sloppy attitude after that, they threw responsibility with you (that's enough, I don't know), and my friend probably realized the importance of taking out an important parent's bicycle.

Future countermeasures include removing the key part of the bicycle and replacing it with a new one, or whether to make reimbursement for that, or whether the friend who lent it to someone without obtaining parental approval is at its own expense. However, even if you change the key and can ride a bicycle, the owner's parents will notice it. Replacing a key also costs money.
You're a middle school student, aren't you? What's that money? Parents are responsible for managing children's money, even if it comes out of pocket money.

After all, it's hard to sort things out without your parents knowing. You can't hide it. Let's report it to both parents and listen to the opinions of adults.
First, let's be honest and report it to our parents.

I'm glad you guys weren't hurt. Troubles are not solved by violence, but by discussion. It's great that we were able to do that (both of them apologized).