When we moved into our new home, my youngest daughter was only a few months old. There was no way I could muster the time and energy to paint murals in the kid's rooms, so I found another cheap and EASY alternative. Have you seen all the options for wall stickers or wallies these days? Walmart, Lowes, Joanns, and Target carry a good selection of kids designs for big and small stickers that adhere and easily come off walls - many in the $10-15 range.
So we have Disney Pixar Cars in the boys room, Winnie the Pooh in my daughter's room, and Dora & Diego in the bathrooms. We arranged some of them to look like wallpaper borders, used them as door decorations and combined collections to make murals. They are so flexible!
Best of all - we can rearrange the stickers whenever we want/need to, and it's easy to change themes in the rooms as the children's interests change. Oh, and it's fun for mom!!