I'm not having children, but I have two nephews and a niece, and when they are old enough to read and use a computer without breaking them, I'm giving them each a netbook preinstalled with ubuntu, various programming tools, and some kind of video chat software so that they have access to me to ask questions at any time.
I want them all to know this kind of thing, regardless of anything else. Plus it will make me the coolest uncle ever.
In my experience delivering Ubuntu boxes to elementary aged children, they are generally unimpressed. This isn't to say you will have a similar experience. I am interested in how to pull it off, so let us know when the time comes.
It has tons of great interactive python programming tools and projects, plus all the hours are logged and you can review how much time the kids spent on each project.
I want them all to know this kind of thing, regardless of anything else. Plus it will make me the coolest uncle ever.