is the room cold? were they on something that could sap heat like a metal bed post or chilled floor? if none of this has happened i'd be a bit concerned that perhaps something is amiss with their circulatory system but for all of them to suddenly develop problems at the same time seems odd. more then likely its something environmental. but keep an eye on things and if start to get concerned take them to the vet for a check up. they shouldn't feel ice cold.
we did have to turn the heating off earlyer as we had a leak humm i never thought of that, they are all normal heat now, or it could of been i had just filled up their water bottols with cold water i dunno it could be a number of things!