I do not, in any way, own Harry Potter. Because if I did, then Dumbledore would control the rotation of the earth... Not that he doesn't.
The Dark Lord stood next to his bed in his ducky pajamas. A fierce look on his eyes. For it was time... to check... TO CHECK FOR DUMLEDORE! Voldemort lay on the floor looking under his bed
His vision was suddenly filled with blue eyes... He froze in alarm, hissing. "DUMBLEDORE. IS. UNDER. MY. BED," he shrieked. He then proceeded to run screaming like a little girl into his dining room where his army of courageous death eaters sat
Dumbledore watched with an amused smile plastered on his ever-merry face. He crawled out from under and spoke, "That never gets old..." he smirked," Hah, checking for me under his bed..." He apparated out of the area.
When Voldemort finally came back with his Death Eaters, the Headmaster was already long gone. "But Bellatrix. He was right. There. I swear on myself...!" he whined. Bellatrix tried not to glare at the visibly stressed Dark Lord.
Back at Hogwarts, Dumbledore was posting pictures of Voldemort around the school. The poster read: "You're scared of this pansy?". The picture had perfectly captured the moment Voldemort screamed.
So Dumbledore wanted to tell his students not to be afraid? Well... no... not particularly. He just wanted to prank Voldemort, and he needed an excuse. So having a school full of children scared and frightened of Voldemort would work just fine for him. And nobody had to know the real reason, right?