Fred II doesn't understand.
He understands the Burrow. Everyone is always happy and laughing at the Burrow, and he has a splendid time with all of his cousins. But on May 2nd, no-one is happy at the Burrow, and Fred doesn't understand.
He understands his house. It's the four floors above the shop in Diagon Alley, and it's a bit crazy, and full of things that explode to the touch. But on May 2nd, nothing explodes in Diagon Alley, and he doesn't understand.
He understands his Aunt Ginny's house in Godrics Hollow, and his Aunt Hermione's house which is right next door. Aunt Ginny's is full of Quidditch kit, brooms, and the smell of freshly baked cakes, and Aunt Hermione's is packed to the brim with books on everything you could think of, and hundreds of photographs of just about everyone he knows. But on May 2nd, there is no nice baking smells and the photographs aren't on the wall anymore, and he doesn't understand.
Fred understands many things. He understands the shop, and how to make his mother give him an extra biscuit, and that two and two make five (he thinks). But he doesn't understand May the 2nd, he doesn't understand it at all.
He understands his mother. She loves him very much, because she says it all the time, and she gets cross with his father because she yells at him sometimes. She can't bake, because last time she burnt his birthday cake, and she used to go to Hogwarts, because she tells him bedtime stories all about it. She hardly ever cries, because she's a 'get-on-with-it' type of person, according to his Uncle Charlie. But he doesn't understand why, on May 2nd (which he's sure is just after May 1st, and she was fine then) she cries a lot, and doesn't even try to bake, and goes to bed very early indeed.
He understands his grandmother. She loves him very much to, because everyone does, and she is a brilliant cook and does nothing but bake and bake and bake and not burn any of it. She gets cross with his Uncle Bill, and with his Uncle Charlie, and with his Uncle Ron, and with his dad, but she loves them very much all the same. He knows that because every time they argue she bursts into tears and tells them she does and that she wished she'd told Fred to. Fred doesn't understand that, because Molly told him she loved him that very afternoon.
Fred understands his Aunts and Uncles. He understands that Aunt Fleur is the prettiest woman ever, apart from his mum, and that Aunt Hermione is very clever and gives excellent hugs, and that Aunt Ginny is funny and affectionate and the best Quidditch player ever. He understands that his Uncle Charlie is brave, because he tames dragons, and that Uncle Ron eats like no-one else he knows, and can do the best impression of Aunt Hermione. He understands that his Uncle Bill did dangerous things with curses, and tells the best stories, and he understands that his Uncle Percy tells boring ones and is best avoided at bed times for that same reason. He understands that his Uncle Harry did something very brave not so long ago, and he doesn't know what it was. But he doesn't understand why, on May 2nd, his very happy relatives stop being happy, and Uncle Bill and Aunt Fleur stay at Shell Cottage, and Aunt Hermione and Uncle Ron go with Uncle Harry to a place very far away, and Aunt Ginny looks sad and stares at the floor, and Grandma and Grandpa look so very lost, which is perhaps the worst bit of all.
Fred understands many things. He understands that his cousin Victoire is cousin Teddy's best friend, and that he isn't to go out of the shop by himself. He understands that his bed is an island, and in the sea around it is full of monsters that are waiting to gobble him up. But he doesn't understand May the 2nd, he doesn't understand it at all.
He understands his father the best of all. His father is funny, and smiley, and happy nearly all of the time. He talks a lot about Fred, and how they did a lot of things together. Fred doesn't really understand that, because he can't remember blowing up a Hogwart's toilet. But then, maybe he was asleep. He understands that his father loves his mother very much, because he's heard him saying it, and he understands that he is looking forward to when his new baby sister comes along. But he doesn't understand why, on May the 2nd, that his father isn't happy any more. He doesn't tell his mother he loves her, he isn't excited about the baby, and he doesn't tell Fred any more stories about what they did together. Instead, he sits and looks out the window, and doesn't smile.
Fred understands many things. He understands that he is a Weasley, and that one day he will go to Hogwarts and be a Gryffindor. He understands that Halloween is sad for Uncle Harry, because his mum and dad died then, a very long time ago. He understands that he isn't to push over his cousin Lucy, no matter how annoying she is. But he doesn't understand May the 2nd, he doesn't understand it all.
It is a very long time before anyone tells him anything that makes any sense. It turns out that the person who his grandmother didn't tell him she loved enough isn't him, but another Uncle. His Uncle Fred. The stories his dad tells aren't about their adventures, but George's adventures with this new Uncle Fred. For a little while, he hates Uncle Fred. He's the one that makes everyone so sad, on May the 2nd, he just knows it. And, if Fred made everyone so happy, then why did he have to go away? Why isn't he here, with them?
The day that Fred finally, properly, understands he is at Godrics Hollow with his Uncle Harry. And Harry tells the story of a very bad wizard, and a very good man, whom Fred is named after. Uncle Harry tells him that the very bad wizard killed the very good young man, but that his namesake didn't go down without a fight. He understands that this Uncle Fred is the one that they grieve for every May the 2nd, and he feels sad. He misses an Uncle whom he never even met.
Fred understands many things. He understands that the sun rises every morning, and sets every night. He understands that the sky is blue and the grass is green. But it is a very long time before he understands May the 2nd, a very long time indeed.