Solid colors are always useful during situations like these, but sometimes those can be boring. Stripes are a great way to still have fun staple items in the room without being replaced in a year. A striped duvet cover can lend itself to any number of themes — find a color that lends itself well to others (for children: red, blue, yellow, green) and you'll be surprised by how easy it is to create look after look around it.
A striped carpet and curtains are also items that will lend themselves to a variety of styles. If you have a circus themed room now, the rugs and curtains can stay when the themed items are going!