I bought our 3 children MP3 players for Christmas (belatedly - after our return from my folks' place in Upper Hutt (near the capital, Wellington)).
These are 128MB Creative MuVo's, which are basically a USB memory device as far as the PC (or Mac) you plug them into is concerned. You just drag and drop mp3 files into the folder (directory) representing the device. If you use something like CDex (from http://sourceforge.net - search for CDex), you can convert songs from your personal CD's to mp3 files which you can then put into the player.
We have tried similar things with WMA (Windows Media Audio) files, with less success - the players supposedly support this, but I think there's some weirdness going on with DRM (Digital Rights Management) - as attempting to load the player device with pre-existing .wma files from Windows Media Player results in that program hanging while trying to 'Inspect' a file - Bah!!
Just dragging and dropping the .wma files into the player folder results in the player skipping or ignoring them... go figure!
Perhaps I'll have to do something drastic like read the manual ;-)
Anyway, .mp3 files converted with CDex from their own CD's, and Podcast mp3's are keeping the children happy at present.
We'll keep an eye on the battery consumption - which so far looks OK - other people have reported as little as 45 mnutes out of an AAA cell - mind you, they did say they liked their music really loud, and the battery life will depend very heavily on the volume (louder music, less playtime). I encourage our kids not to blast their ears out...
OTOH, others have said 12 hours :)
Matt reckons he has probably had 7 hours or so playing time so far... not that we're measuring it scientifically. We're still using the batteries that came with the players.
The sound quality is pretty good with the supplied 'bud' earphones.