If you or the children do get norovirus, @Ansumpasty, could you just freeze as much as possible of the Christmas food, and postpone Christmas until you are all feeling a bit better?
I don't blame you for being stressed about it - no-one wants norovirus at the best of times, and we do put in a lot of effort at Christmas to make it a wonderful time for the family, so no wonder you are more stressed by this worry.
I well remember one Christmas, when the dses were children. Ds1 was about 7, and the other two were 5 and 3. We told them that we would come downstairs and open stockings at 7.30am, and they could come and wake us then if we weren't already awake, but not before. On the dot of 7.30am, they all trooped in, and ds1 said "Happy Christmas mum and dad - I've been sick three times!!" - he had been very literal about the 'but not before' bit. We should have explained that he could wake us earlier in an emergency.
Anyhow - he spent the rest of the day in a cycle of vomiting, sleeping, waking up feeling a bit better, opening some presents, and then being sick again to start the cycle all over. In the meantime, dh was starting to feel ill too, and I was splitting my time between cooking Christmas dinner, and looking after ds1, so ds2 and ds3 were left to their own devices quite a lot of the time - and so they spent their day eating as much of the chocolate they'd been given as possible.
All this meant that, by the time we got to eat Christmas dinner, ds1 was asleep, following another bout of sickness, ds2 and ds3 were full of sweets, dh was feeling nauseous and didn't want to eat anything, so the only person who ate any Christmas dinner was me! I'd have been better off with McNuggets - it would have been less effort!
Despite all this, it is one of the Christmases I remember best.