When the pigs fly? Sure, they have already started doing that!
I guess my daughter is a bit too old for such games, but she still wanted to fly the piggy to the moon before she left for kindergarten.
It must be one of the easiest Do It Yourself toys. And the variations are countless. To name a few: caterpillar going for apple, strongman with outstretched arms flying up, bird flying up to a cloud and many many more.
This is how it looks on the back side. The most important detail is the drinking straw. The thread must go through it. Also it is important to have some kind of stopper/handles on the both ends of the string (you can cut out two pieces of the same paper). Otherwise the rocket would just fall to the floor.
You need to play with the length of the rope. Don't make it too short, as the trip will take less time, and don't make it to long as the child will never be able to reach the goal. What fun would that be?
Unless you're one of those who tells the kid life is hard and he can't get everything in life. I hope not!