As your daughter's obsession with Hannah Montana matures into a love for Lady Gaga, she'll be quite ready to rid herself of all of the Hannah décor. Your son may love Transformers and dinosaur posters for years to come, or he may not.
You can expect a steady evolution of changing artwork over the next few years, so plan a room that will accommodate this. Skip the framed posters and prints, and instead, create a corkboard wall. This will allow your tween to decorate with photos and drawings of the moment that easily can be changed each time he or she gets a new wave of inspiration.