4(Black Clover)

An Au were the Black Bulls(except Yami...and Henry since he can't go on missions) plus someone else at the writer's choice go on a mission only to have the other person suddenly call for help as while they were able to deal with whatever the mission was, the Black Bulls were all turned into kids(between 1 to 5 year old).

Cue Julius and the Captains having to take care of them as their squads try to find a way to get the Black Bulls back to their normal age.

Why Julius and the Captains? Because I think it would be funnier with them especially in case a someone tries to fuck up things.

Would it be all for all or divided? I would go for divided mostly because I have thought on how it would be divided.

Gordon would be on the care of Kaiser simply because they both are mostly ignored or pushed to the side so it would be good to give them more screen time and have them bond.

Noelle would obviously be with Nozel but also Jack because while Jack was taking care of Gauche he accidentally finds a crying Noelle and decided it was better for them to take care of the children together.

Luck would be taken care of by Charlotte mostly because I do like the headcanon that they are half-siblings and it would be interesting to see how a sibling relationship would be like between them.

Grey would be with Rill who despite being a teen I think would be able to get Grey to be a more open and a bit less shy(but that may be only me).

Magna and Zora would be in Fuegoleon's care as he already dealt with raising a fire prone child, he could deal with another one and I think be a good person to take care of Zora.

Vanessa would be the care of the only other witch they all know, Dorothy, mostly because they deserve more time together and bonding even if it is with a kid Vanessa.

Charmy would be taken in by William, simply because I believe it would be an interesting dynamic.

Asta and Nacht would be on Yami(and maybe Henry)'s care because he was basically a parental figure for Asta and it is funny to have Nacht be taken care by the person he 'hates' the most.

Lastly Finral and Nero would be in Julius and Marx care as I think Julius is the best choice to help Finral with his insecurity when it comes to his magic and to deal with Leonor and Liliane if they try anything while Marx seems to be a good choice to care for Nero.

Also, all the kids have the memories of their kid self at the age the writer choose them to be.

Anything else is up to the writer.