Hi guys, I'm newbie to Malifaux, and french.
About your question, oddly enough, "gamin" is named "rejeton" in the french Malifaux sources, whose most accurate english translation is "offspring".
So as far as it matters, I'd recommend to stick to the english pronounciation for the gamin word.
for the fun's sake, one french site displaying the odd translation:
http://forum.alchimiste-games.fr/viewtopic.php?pid=15108