Disclaimer: I don't now nor is it likely I will ever own Harry Potter
"Excuse me." Harry Potter gaped at the strange girl and boy in front of him. "But… who are you again?" The boy puffed out his chest. " I'm August Jake Romeo Potter and this," (He jerked a thumb to the girl) " is my sister Abigail Jasmine Juliet Potter, we're your cousins from America."
That put Harry on Guard.. "I don't have cousins in America! I only have one cousin and you're not Dudley Dursley!"
This caused the girl Abigail to sneer "We've come to help you defeat your evil parents Lilly and James Potter, that spoiled brat of a princess your sister Rose and that medalling old fart Dumbledore…" But she was interrupted.
"Ah, Mr and Miss Potter you're here rather early." The three teens whirled round to face Albus Dumbledore Headmaster of Hogwarts school of witchcraft and wizardry. "Please come into my office."
He ushered them in, but stopped Harry. "Don't be angry with them Harry. If anything you should pity them." Before Harry could ask why, Dumbledore shut his office door and locked it. Turning to the collection of students outside his office Dumbledore proclaimed. "Well what are you all sitting around here for, it's a beautiful day the sun is shining and… I have cancelled all end of term exams!" The students screamed with joy, and ran outside to enjoy the wonderful sunny day. Harry slowly followed them, taking a last look over his shoulder before he too disappeared down the stairway.
Albus Dumbledore waited a few minutes until the childrens' footsteps faded away. Then he unlocked the door to his office, and slowly stepped inside.
His office was in disarray. The fragile objects that had taken him decades to collect were broken and scattered all around the floor, his once magnificent desk was now just a pile of fire wood and in the middle this disaster zone lay two gibbering beautiful teens and sitting on them was a very small angelic looking toddler.
Dumbledore sighed and picked the child up. "Oh Tristan, it's the only way we can deal with these intruders. The boy laughed evilly. Dumbledore just shook his head sadly.
Perhaps it was irresponsible to encourage the boy in this way. But on the other hand young Tristan had all but eliminated their Mary Sue problem.
At any rate it couldn't possibly make the boy worse. Could it? No, the young Muggle was just in a destructive phase. Best just to let it take it's course, and if they took down a few Mary Sues on the way, where was the harm in that?