Children's rooms and nurseries weren't always the light, airy places we strive for today. It wasn't until the 20th century that decoration of children's rooms became popular. Before then art on children's rooms walls was likely to be based on bible stories, or simple silhouettes illustrating children's tales. Often stitching samplers illustration bible verses formed the main decoration.
If you are working on decorating a dolls house nursery, try to find period appropriate illustrations to use on the walls. If that isn't an option, turn to your digital camera and photo software to make silhouettes. Cut paper silhouettes were popular long before photos, and printing presses made lithographs and Victorian scenes widely available. You can easily make silhouettes of family members by taking a side shot against a plain light background, then changing the contrast and brightness levels in your photo software to create silhouettes.
Need more modern touches in your children's room? Take photos of actual children's art (your own preferably) and reduce it to a size that fits on the walls of your dolls house scene.
Sources of illustrations and silhouettes suitable for use in a dolls house nursery or child's room can be found in many locations. Web Clip Art has a great collection of silhouettes, Antiques have collections of Halloween postcards and other vintage illustrations. Graphics Software have tutorials on making photo frames in various types of photo software.