I had a few growing up. They are awesome little pets, so personable and sweet. I'd def get two females, males have gross pendulous nads, can be stinky and might fight. I use aspen shavings with my bunnies, makes less dust than that newspaper stuff but doesn't have phenols in it. You have to cut their nails periodically as they don't really wear down like a rat or hamster.
Also I'll just leave this here....
http://cuddlycavies.homestead.com/morecostumes.html
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they are the reason i grew up to love collies.. their white stripe and reddish sable fur.. first dog sheltie..then normal size collie.. but it all started with my Guinea pig who looked like lassie..lol........ your daughter is adorable and so happy.. happy birthday girl.