I think Dick would be bullied for his accent so here's how he got his American one. Reverse!Batfam

Dick: 8
Jason: 13
Tim: 16
Damian: 18

EDIT: TW BULLYING

https://www.bullying.co.uk/

https://www.nationalbullyinghelpline.co.uk/contact.html

https://www.anti-bullyingalliance.org.uk/tools-information/if-youre-being-bullied/find-help-and-support

There was something off about the youngest member of the household when he started to go to school. Each day he'd start off being chatty but when he got home he'd be deadly silent. Bruce called the school to ask why he wasn't talking and the school simply said they thought he was a mute. The teacher said he had opted out of speaking and written on a piece of paper that the trauma of life had made him go mute. Bruce told the brothers this. They couldn't believe that the boy who practically ran his mouth like a river could be so silent. That wasn't the weirdest thing, however. A few months later and Dick was silent at home but very talkative at school. In fact, he had been rewarded for answering and explaining the most questions correctly. So now they had a different problem. He was silent during his time with them. Silence was deadly in their line of work and they were worried about the effect it might have on their patrols. 

Then Dick spoke. They thought they'd be happy when he finally broke this need to be silent at unimportant times but they couldn't be. It wasn't Dick speaking. "Good morning everyone," Dick had announced with a bright smile. He looked rather proud of himself. Proud the family wasn't. They were all caught off guard. This was because the accent they had grown to love was gone. It has been killed, smothered by an American accent that matched theirs. They had been at breakfast when it happened. Damian and Bruce dropped their newspapers at the exact same time, Alfred almost spilt the orange juice, Tim choked on his water and Jason had actually paused eating. He paused eating. Now it was serious. "Say that again," Bruce said quietly. He didn't believe his ears. Dick cocked his head a little in confusion but repeated the phrase although it sounded more like a question. He sat on the seat closest to Tim and looked at them all in confusion. Why had they reacted like this? Had he said something wrong? "What happened to your accent?" Damian asked, finally collecting his thoughts. 

"What accent?" Dick asked. He knew what accent they meant but he was hoping they'd give up asking questions if he was difficult. They didn't. "Your accent, the Romani one. What happened to it?" Tim clarified. 

"I have no idea what you're talking about," he replied.

"Richard, tell us what's going on," Bruce ordered. Dick didn't flinch. He kept up his clueless act.

 "Nothing is going on." They now noticed the slight hesitance he had before he said every word. Something was ever so wrong and they weren't leaving the table until they found out what it was. "On the contrary, there is. Why aren't you using your accent?" Damian insisted. If Dick wanted to play the long game he'd show him. He'd show him that he could play longer and better. "You're all going insane," he said before covering his mouth. The old accent had slipped through the cracks. He hadn't practised well enough. "Ha there it is!" Jason shouted triumphantly. 

This caused Dick to tear up a little bit and look distressed. "Don't say that!" Dick shouted back, his accent clear. It was revealed by his anger and he quickly returned his hand over his mouth. "Are you crying?" Jason asked, feeling guilty now. He had just gotten a little excited that's all. Dick shook his head furiously. Alfred put a plate of food down in front of Dick but the boy didn't even look at it let alone eat some of it. Whatever was bothering him was big. Bigger than a simple phase. Something had caused this. "I thought you liked your accent," Tim stated. Dick shook his head, mouth still covered by his hand. "Why don't you like it anymore?" He hesitated.

"Someone said a mean thing about it didn't they?" Tim continued. He'd struck metaphorical gold at this point and he wasn't stopping. "You can tell us, Dickie." 

Silence. Then Dick broke down in tears. Bruce shot up out of his seat and pulled his son into a loving hug. "It's alright chum, it's alright. Can you tell us what happened?" Bruce asked, sitting on a chair with Dick in his lap. The poor thing was crying his little heart out into his chest. "They said it wasn't right," he managed to say through broken sobs. "They said no one likes foreigners. They said I should go back to where I came from." A fire was lit in all their hearts. Bullies. Of course, it had been bullies. How hadn't they seen the signs? On a more serious note, how did the teachers not see the signs? One minute a kid is mute the next he's speaking with an American accent. They should've called. They should've done something.  "I can't go back to where I came from Bruce! I was born between borders!" he exclaimed. Bruce shushed him gently and rocked him back and forth slowly. "You should've come to us Grayson," Damian stated with a hint of empathy. He was in the same boat as him in a way. Although he had a white dad, his mother wasn't white. He was interracial and got a lot of bullying for it. He understood Dick's pain and felt hurt they, he,  wasn't there sooner to spare him of it. They couldn't take back the words the bullies said. Those words would stick to him like he was glue. Dick shrugged solemnly. "I don't like my accent, I wanna be like you guys. I don't want it!" Their hearts broke. He wanted to destroy this part of himself. "But your accent is who you are," Tim reasoned. 

"I don't want it to be! I want to sound like this family. I want to fit in." Bruce didn't know what to do. The brothers didn't know what to do. 

This time Alfred stepped in. He picked up the young boy and sat him on a chair. He then kneeled down to his eye level. "I don't want any more of this silly accent business. I have a British accent do I not?" he asked. Dick's eyes were fixed on the floor but he nodded all the same. "I don't sound like Master Bruce, do I?" he asked. Dick shook his head. "If you listen closely to how Master Damian speaks, does he sound the same as Master Jason?" Dick shook his head. "An accent is simply something we have that is environmental. Your accent is mixed with many because you've picked up so much from your travels. Mine was created because I spent most of my life with people with the same accent as me." Dick looked up a little bit. "But what if I don't want it? Plenty of British actors fake an American accent," Dick reasoned. 

"And in interviews do they sound British or American?" Alfred asked. 

"British." he admitted defeatedly. "But they're doing it for a job. I want to sound American. I want to sound like I belong."

"And you do belong, Master Dick, no matter how different you sound or look. You're part of our family." Dick smiled but it was clear the message hadn't gone through. He carried on using the American accent he'd fashioned and they couldn't stop him. The accent only came out when he had an extremely negative emotion. They just wished they could go back in time and change the damage.