Author Note: I'm getting organised and putting some older fics on .
April Fools
The first time they swap jumpers is on their eighth birthday.
Mum and Dad think they don't listen to the lectures and the lessons, because they don't finish the work or they make jokes about what they've been told, but with four ears between them they take everything in.
Dad always does the lessons on Muggles, after he's come home from work. April Fool's Day is a Muggle tradition when people make jokes in the morning and then tell people what they've done once it's midday. All of them sit around the front room whilst he tells them about this other culture and that Fred and George were born on April the first, and everyone laughs.
It's appropriate for them, and even more appropriate that they play a joke, so they swap jumpers; Fred becomes George and George becomes Fred.
And no one notices.
People had gotten them mixed up before, even Mum, but they didn't realise how often it happened until they mixed things up further. They might look the same, but apparently no one but Fred knew that George always sat next to Ginny at meal times and no one but George knew that Fred always ate his eggs before his bacon. It came as a bit of a shock that the little things that made Fred Fred and George George weren't noticed by anyone else.
First it was annoying, then they did what they always did and laughed it off. They made it into a joke, created Gred and Forge, deliberately dressed the same. They didn't tell anyone that the wrong boy blew out the candles on the wrong cake and that little Ginny gave her paintings of your favourite things to the wrong brother, even though she got their individual favourites right.
Contrary to popular belief, although they deliberately confused people they never deliberately switched again.
(Although George wishes they had.)