Did you started teaching your kid How to use a computer ? Then why not make a new user account for him ? You know kids need cute things and they love things they are attached to.And we are all need our kids more and more happy.
My neighbor came and asked me to customise his desktop for his Kids.I had no idea where to start, then I tried changing his wallpaper and the kids started loving it.They were talking about the cow and the animals in those images and yeah they really loved it.
You can find those images at www.pixelgirlpresents.com.
The site is not specifically for Kids, it is for all. And it has a lot of illustrations and artworks to download and they are all free.
Need more advices on how to setup your kids Desktop (Let it be any OS), just drop an e-mail at nextdoornerd AT gmail DOT com.