I've just trawled through all the system fonts on my Mac but can't find anything to match. I'd agree with eldridge in that it's pretty close to VAG Rounded, but to me, it actually looks a bit 'hand drawn' so don't know if you'll find it or not? Best of luck though... I know what it's like with print deadlines.
 When I say 'hand drawn' I mean they've perhaps taken a font in a design app. and stroked it or created an offset path to get the balloon effect on it, so whilst it's been made from a regular font, it's actually been bastardised. I could be completely wrong though - has been known before (a lot) - so please don't let me lead you down the garden path. Again - best of luck with it.