Accidental Children

Harry and Neville somehow ruin their potion in such a way that makes it gaseous, and before Professor Snape can get rid of the contents, Draco, Hermione, and Harry breathe it in. It has the unfortunate effect of de-aging them to five-year-olds. COMPLETELY AU! VOLDEMORT IS DEAD AND GONE NO HORCRUXES, DUMBLEDORE IS ACTUALLY A SORT OF OKAY PERSON, MALFOYS AREN'T EVIL.