I'd personally pick up a netbook from a Best Buy or simliar store that offers a warranty program against accidental damage (dropping it, stepping on it, etc.) Netbooks are pretty cheap, and aren't super powerful, but can easily handle email, word processing and that sort of thing, plus they have a regular keyboard for typing.
There are several types of software you can install to lock down the system, and Windows 7 comes with some built-in security tools as well to prevent children from launching programs they should not (you can even define hours of use.) The folks at the support desk at Best Buy can help you, or if you know someone good w/computers they can walk you through it. (I work in IT, btw.
