Try striping one accent wall or all four walls. Alternate two colors -- or three, if you're daring -- in the striped pattern of your choice. Create heavy stripes or thin pinstripes. The stripes don't have to be straight. Consider wavy stripes or a zebra effect. Choose contrasting colors or the same color in different shades, deep gray and light gray, for example. Before you apply your stripes, give the walls a fresh coat of paint. Use painter's tape to make straight lines, if that's the look you're going for.
Use a sponging or rag technique to give your wall a subtle dimensional look. Use two or more colors to create the effect. Paint the walls a neutral color, and allow it to dry before lightly sponging on a darker color. If you want to add more than one color, apply each separately, and allow it to dry before you apply the next color.
Work with your daughter to create a mural or designs on one wall. Decide what you want to do, and give the wall a fresh coat of paint. Pencil the design on the wall, and then paint it in, using small paintbrushes. Alternatively, hand paint a border around the room.
Use glazing to create a rich wall treatment. Start with white or off-white paint as a base, and build thin layers of tinted glaze, allowing them to dry between applications. While each layer is still wet, use a brush to blend the glaze, spreading it evenly but allowing the brush strokes to show. Continue applying the glaze until you have reached the desired richness.