So what happens to those balloons that fly away into the sky?

Like those balloons that we lost when we were children or the ones that strayed away at a party or a carnival? Where do they go? Do they just slowly float down and land somewhere with nothing? Do they fly into space never to be seen again? Or what if millions of years from now, we go into space and find a planet made of those balloons that we lost as a child. Wel call it the planet of broken dreams