While most adults' bedrooms have solid-coloured walls, kids' walls are a lot more fun if there's a colourful mural, or at least a few designs. One perennial favourite is a rainbow -- almost anyone can paint one, regardless of their level of experience. While elephant, puppies, and even clouds and hills require either a stencil or a certain amount of artistic talent, painting a rainbow is a simple case of geometric shapes and solid colours.
Paint the wall a solid colour. Wait a day for it to dry.
Drive a small nail into the wall at the point where you want the bottom centre of your rainbow to be, and tie a long string to it. Tie a piece of chalk at the other end, as far along the length of your string as the outer edge of the future rainbow.
Draw an arc with the chalk, pulling the string taut as you form the shape of the rainbow. Shorten the string and repeat for each coloured stripe you want your rainbow to have. Mark the horizontal bottom edge of the rainbow, using a spirit level to make sure your measurement is accurate.
Fill in the spaces between the concentric arcs with paint. If you want a distinct, cartoonish rainbow, use bright colours and wait for each to dry before adding the next to prevent smudging. If you want something more realistic, water down your paints and mix the colours at the edges as you paint the rainbow, using a damp rag to blend them further.