I honestly don't know but it's High-school au Xiaoven!

Xiao's background

this is my way of explaining Xiao and Ganyu's background I'll Probably do Hu Tao's and Venti's soon.
As kids Xiao and Ganyu always knew Zhongli as papa Childe as dad. They always wondered why other kids called their parents Mom and Dad considering they weren't aware of how different their life was.
There was this lady that would constantly come to see them. She had long brown hair that faded to blue. Ganyu always thought it was because of water and would constantly dip her head in any clear blue water she came near thinking it would keep her hair the light blue it is causing Zhongli and Childe to panic greatly.
Soon after it continuously happened they explained to Ganyu that her hair wouldn't change color is she didn't dip it in water. Xiao was always distant from people and would almost never leave Zhongli's side. So you can already imagine how difficult it was for Him and Childe to leave him at preschool by himself. He'd usually run off but then came the day Childe had to drop him off. Everything went smoothly until Xiao noticed Childe was attempting to leave. He tried staying closer to him watching his every move but him being a kid he got distracted by something allowing Childe to sneak away.
Xiao did not like that at all causing him to burst into tears shouting for Childe to come back. Xiao noticed the door was open and tried running after Childe but the teacher closed it in time upsetting Xiao even more.
They managed to calm Xiao down until it was time to go home. He was too busy playing by himself with blocks to even notice Childe enter the classroom. Once Childe apologized to the teacher and got Childe Xiao forced him to promise he'd never leave him there again.
Ganyu on the other hand enjoyed going to school or well technically daycare. There was one near the place Childe worked so when Zhongli had Xiao Ganyu would be there while Childe worked. She enjoyed helping the other kids and playing even though she was the smallest one there. The ladies that worked there described Ganyu and helpful and smart for her age. She was also known as sleepyhead Ganyu due to her falling asleep in random places at random times.
Childe and Zhongli always knew they'd eventually have to tell the two that Guizhong was their mother but they didn't really know when. But once Xiao was eight and Ganyu was seven they felt they were old enough to know.
Now for how they got Qiqi because why not she's apart of the family too. Not too long after telling Xiao and Ganyu about their mother Guizhong agreed to watch them whilst Childe and Zhongli went out. They decided on a nice restaurant it was a nice night even though it was raining.
As they were walking down the roads Zhongli heard a faint cry of what sounded like a baby and Zhongli being Zhongli he went to investigate.
He discovered Qiqi in what looked a bunch of soaked towels not to mention her clothing was also wet. From what the doctors said it was a good thing Zhongli was there and had an extra jacket our else Qiqi would've died from the cold. They also discovered a cut on her forehead *which is now covered by her bangs*
However their discovery of Qiqi caused them to be out a lot later than they planned and told Xiao and Ganyu causing them to worry.
But once they got home they explained everything including how they have another sibling.