I wonder, since MCE is supposedly just a modified version of XP Pro if you can do a repair on the kids system to activate it with the version you found that needs no activation. With XP Pro anyway, I can boot to the cd, skip the first mention of a repair (console) and go on as if I'm doing a regular install. Then when XP install gets to the point where it scans for an OS it find XP already there and asks if you want to repair press R. This second repair is non-destructive and will keep all your data and programs intact but you loose all your critical updates (not on the disk your using already) because the system files are replaced with the originals on the cd. Having little experience with MCE I don't know it it has the same option but if you use a different disk the system is replaced and the activation would go away. You can always F3 out of the bootup install at any time if you get nervous, up to the final window where it will install anyway. You just have to follow any instructions that come with the new disk, like "do not enter a serial" etc. and the rebuilt OS will be from the new disk not your old one.

It couldn't hurt to try, as I said you can always F3 out if you think the second repair option is not there. In my XP Pro it comes directly ater you hit F8 to accept the license agreement and the disk scans for any OS already present. If your only option at that point is to install with no repair option then your out of luck.

Even XP Pro disks fail the non-destructive reinstall if they have been heavilty nlited with drivers and extras. If you nlite SP updates only (SP2 SP3) it seems to be OK.