While staying at the Weasleys during the summer, Ron and the other boys get in trouble for something. I have tagged all the Weasleys but you don’t have to include all of them. This can be up to you. Harry tries to cover for them but Molly witnessed what it was and gently scolds Harry for trying to take the fall. Molly punishes the boys (not Harry) with chores. Harry tells the boys they got off lightly because he would’ve got a whipping with a belt (thinking this is normal).
The extent of Harry’s abuse is discovered and the Weasleys want to adopt Harry. Unfortunately Dumbledore in his infinite wisdom, makes Snape take care of Harry instead. Snape is a bit of an ass and first refuses to not see Harry as the devil incarnate and at first treats him harshly. Gradually, he sees Harry for who is.
Please do not have CP (including mouth soaping) as part of this story. In fact, you could mention its illegality (an idea not mandatory). Harry can expect it from Snape, even assuming that would be his punishment for something. However, it shouldn’t be used. Anything else is fair game. Can happen at any year at Hogwarts.