Balloon Kid

Balloon Kid is a unique side-scrolling platform game. You control a little girl who's brother has floated away on a big bunch of balloons. It's up to you to chase after him through 8 treacherous levels. Instead of the usual jumping from platform to platform, you have a pair of balloons that allow you to float through the level. You must control your height carefully by tapping the 'A' button. Meanwhile, the screen is always scrolling to the left, and you have to keep up. (mobygames.com