Wired has a nice article on how to build your own cheap linux-based computer for $150 minus the monitor, keyboard, and mouse (http://howto.wired.com/wiki/Build_a_$150_Linux_PC). It's not exactly a computing powerhouse, but it'll handle simple tasks. If your kids are asking for a computer, this could be a fun project to work through with them. They can help buy the components, assemble everything, and install the operating system. It'll give them a much better appreciation for what a computer really easy, and it'll be easy on your wallet too.