It sounds beautiful! I painted an underwater mural for my twins' room, you can see photos http://a5.sphotos.ak.fbcdn.net/hphot..._6502910_n.jpg http://a1.sphotos.ak.fbcdn.net/hphot..._2460672_n.jpg http://a2.sphotos.ak.fbcdn.net/hphot..._3553894_n.jpg http://a8.sphotos.ak.fbcdn.net/hphot..._5957544_n.jpg http://a5.sphotos.ak.fbcdn.net/hphot..._3301912_n.jpg Some of it was freehand but I am not a great artist so I went with stencils for the fish, mermaids and shells, using a blunt ended brush to dab the paint on. Since those photos were taken there are clouds and birds in the sky (white paint applied with a sponge for clouds). Bunnings have a great range of paints and brushes.

I have also done a mural for DS1's room, which is a midnight blue with back motocross stickers (it looks like they are all jumping their bikes) and silver stars in the sky. Again I used stencils for the stars but I spray painted them on which looks awesome. For the details I found less is more, so there is a lot of space on the wall that is not covered with stars. Stickers can be a great addition to a mural, combined with paint, and there are lots of companies that sell vinyl stickers at a great price. Ebay is a great place to look for them, even just for ideas.