You think for a moment, then come up with an idea and say, "Genie, I wish everyone in the world was a little kid, and none of them would remember life before the change, except me."
"It is as you wish." the genie replied, and with a quick twitch of his nose, everything started to feel different.
You started to shrink and grow smaller. In a few moments, your clothes were like a tent and the shrinking had stopped. Climbing out of the oversized clothes, you look down at your naked body and see that you look to be no older than five. You were small back then!
"Heh heh, thanks genie."
"It is my pleasure."
Before you make your second wish, you decide to look around for a little bit to see how others react. You quickly run upstairs to get some fitting clothes, but when you arrive all that is left are you adult clothes.
Well, since everyone else is in the same situation now, you wonder what the heck, and leave the house in the nude.
Everyone in the entire world has been regressed in age. The oldest pereson you saw was maybe seven or eight. Like you, no one else seems to be wearing any clothing. After all, children are somewhat absent minded, and there are no parents to remind them to get dressed, or to buy the clothes from now on. So everyone is naked, which probaly isn't good news for the fashion industry. Then again, there won't be anyone to work either.