Shinichi knew he had to face this situation at some point

Sign of Friendship

Detective Conan (c) Gosho Aoyama

Shinichi knew he had to face this situation at some point. He just didn't expect it to be so soon.
Right now Ayumi was looking at him with a serious expression. Well, as serious as an 8 years old girl could look.

It was a warm, gentle spring day, the last days of the school year. These were the last few days for Shinichi and Ran on Teitan Highschool. And the last days of the second grade for Ai, Ayumi, Genta and Mitsuhiko. Since tests were over already, the six of them had decided to celebrate their successfully mastered school year at Tropical Land.
He knew Ayumi long enough now – both as Conan Edogawa during his second childhood and as Shinichi Kudô after his return – to notice her change in behaviour. She was looking at him when she thought he wouldn't notice. Her enthusiasm for the fairs attractions had suddenly disappeared. She seemed to gather courage to confront him with something.

"Ayumi-chan, you look a bit tired", noticed Ran before Shinichi had the time to take the initiative to suggest anything himself. "Let's take a break and get something to eat."
Ran smiled reassuring and pointed at a snack bar ahead. So he hadn't been the only one perceiving Ayumis change in behaviour.
"Look, there is a group leaving", Mitsuhiko called and pointed at a group of five teenager leaving one of the tables where the snack bars customers could eat their meals. Both Mitsuhiko and Genta were running towards the table claiming it before any other park visitor could do the same. The warm weather had already allured many visitors in the amusement park and it seemed to be getting fuller and fuller every minute. A huge crowd was already waiting in line before the snack bar. Tables and chairs to sit on were scarce.

The next moment all six of them were sitting on the table. However there was still that long line in front of the bar. "Ayumi you can get some rest and keep the seats while the rest of us gets the snacks", Ran finally decided and stood up, ready to line up.
Just when he, Ai, Mitsuhiko and Genta wanted to followed her example, Shinichi saw Ayumis eyes lit up for a moment. It was that special sign that she had made up her mind.
"Shinichi-niisan, can you stay here with me?" she said determined. "I have something to ask you"
Shinichi shrugged and sat down again while the other four went into the line. Now he knew for sure he wasn't just imagining things. Ayumi really wanted to talk with him.

…
However she remained silent for a long time. She seemed to be examining him, scanning him. Finally she started speaking.
"Here is your jacket", she said and was handing Shinichis jacket over the table in his direction. He remembered – he had taken it off before he entered one of the rollercoaster together with Ran, Mitsuhiko and Genta. He had given it to Ayumi who had to wait together with Ai since both weren't tall enough for that ride yet. Thinking of it – Ayumi started behaving differently right after the rollercoaster ride. But why?

"While I was holding it I noticed something in your pocket", Ayumi continued. "Something hard and very small…"
Shinichi faltered for a moment. Small and hard? There was only one such a thing he could think of… absent-minded he pated the inside pocket. It was gone; the small hard thing was gone. A look in Ayumis face told him she noticed that he knew what was missing.

"Here" – Ayumi gently put the small object on the table. He was right: It was the old Detective Boys badge. HIS old Detective Boys badge.
It was one of the few things that he kept from his time as Conan Edogawa. When he got the antidote he left without telling the three kids the truth. To them Conan went away with his parents. Only Ran knew. That was over one year ago now.
He wasn't still sure why he had kept it a secret from them. Maybe it was because of Ai - he didn't want to destroy her new life as a kid with real friends. If they ever found out that he had shrunk and assumed the identity as Conan Edogawa they might start suspecting Ai as well.
Or maybe he was afraid that they would think their friendship was just a fake. Both the old friendship between them and Conan and the new friendship between them and Shinichi now… No. He couldn't tell her the truth.

"Why did you have it in your pocket?" Ayumi asked since Shinichi didn't say anything. Instead he glanced at the line in front of the snack bar. Ran and the others were still waiting. They wouldn't get back to the table to save him anytime soon.
Yeah, why did he have it in his pocket? Was it just - as he kept telling himself - in case if the four remaining Detective Boys got into trouble so he could contact them? Well, it was more than that. It was a sign of friendship. A friendship he had become quite fond of during his involuntary second childhood and that he could re-establish after Shinichi Kudôs return.
But of course he couldn't tell her that.

"This is Conan-kuns badge, right?" Ayumi was still looking at him, waiting for an answer. "It still has that dent when it felt down during that case…"
She was right. It still had that unique dent. No chance denying that it wasn't his. "Conan-kun… he gave it to me", Shinichi finally said, with the only excuse that was coming to his mind that moment.

"Lie!" Ayumi exclaimed. Shinichi looked at her; he had avoided eye-contact with her since she had shown him the badge. And he was surprised.
She wasn't mad at him. Quite the opposite, she had a triumphant smile on her face. "Conan-kun would never give his badge away."
She was right. She knew Conan way to well to believe in such a simple lie. He would not be able to talk her out of this. He felt cornered – just the way he imagined the criminals sometimes felt when he deducted step by step how they committed their crimes.

Ayumi didn't seem to have given up yet, although Shinichi remained silent. She had one trump left… one of Shinichis weaknesses.
"Do you know the famous saying of Sherlock Holmes?" she asked innocently. Shinichis interest returned immediately.
"When you have eliminated the impossible,…" Ayumi began.
"…whatever remains, however improbable, must be the truth", Shinichi completed the sentence. "It's one of the most famous quotations from the Sherlock Holmes novels." Discussing Holmes was far more enjoying than talking about the Detective Badge.
Ayumi nodded.

"It's impossible that Conan-kun would have given away his badge", she finally exclaimed. "And I don't think you would have taken it from him"
Shinichi halted abruptly. She was applying the Holmes quotation on the badge now. He had just walked into the trap of an 8 year old elementary student.
"So the only thing that remains…" Ayumi continued, her voice beginning to tremble. She was still looking at him expectantly.

Shinichi started smiling. She had learned so much. Maybe he was wrong… maybe it wasn't wrong to tell the truth after all.
"There is only one truth", he encouraged the little girl. "And it's up to us detectives to discover it."
"So it is true?" Ayumi asked, gathering her courage one more time.

"Shinichi-niisan, are you Conan-kun?"
There was no trace of distrust, hostility or anger in her voice.
Just curiosity and a little bit pride. His fears didn't turn true. Nothing had changed. They were still friends.
Shinichi nodded, confirming that she was right with her deduction.

Ayumi didn't answer, although it was apparent that she was slowly realizing what her deduction meant. Shinichi guessed she would have a lot of questions for him now. And he owed it to answer those questions. Not only to her… to Genta and Mitsuhiko as well. Carefully he picked up his Detective Boys badge and slipped it safely back into the inner pocket of his jacket.

Before Ayumi could ask any questions, Ran and the other three Detective Boys returned, chatting happily, their hands full with drinks and food.
"I will answer all of your questions later", Shinichi said to Ayumi quickly. "For now, let us just enjoy the beautiful day."
Ayumi blinked, and then started smiling again. She didn't have to answer; her approval was evident without the need for words. It was not like anything important had changed.

A/N:

"What would happen if Ayumi found Conans Detective Boys Badge in Shinichis pocket?"
Some inspirations just WANT to be written down. And I think it came out well.