kids have a higher body temp than we adults and can take cold better.
i havent brought my girl to a winter country before. but she can sleep in shorts n short sleeve shirt in a AC room of 18-20degs (sometimes with fan at full blast) and not cover blanket to sleep when everyone else is freezing already... well sometimes i think she is like hibernating. =X
anyway, just wear thicker clothes for your child (ie, get winter clothings) shld be good.