I need bathroom design advice...

Kimberly
We have the tiniest bathroom ever and it needs to be shared between my three stepsons and our daughter who will be here in January AND it's the bathroom any visitors to the house use. I am at a loss of how to design it and make it functional for everyone without being too kids oriented. It needs to be functional for kids and teenagers, but not scream kids bathroom. Any ideas? Oh, and it's tiny. Likw, the size of a closet. And no storage. Ughhhh. Helppp!