If you want to teach the kids to use a computer and tools such as a word processor, spreadsheet, presentation software Open Office (as iscanut suggests ) or IBMs Lotus Symphony click here (also free) are great choices.
If they *need* to Office why not look at the Office Web Apps click here - At least before spending any cash. They are not fully featured. (I have no experience of these so cant say how good -or not- they are)
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