I would spoil them rotten, I think is the simple answer.
We'd start the morning with my speciality cheese on toast (a Dizzo household Christmas tradition), then adjourn to the living room where we'd exchange gifts while listening to cheesy Christmas tunes. We might even have a little sing-song - with Jensen's singing voice, not Dean's!
Afterwards, we'd go for a long walk around the country park in my village, and work up a good appetite for the Christmas dinner that we'd cook when we got back home. My kitchen's small, so it'd be nice and cosy, the three of us working in there together.
Christmas dinner would be delicious and satisfying, with candles, crackers and silly hats and there would be enough for second helpings for Dean (and Sam, although he'd use the excuse that he didn't want anything to go to waste) and we'd round it off with pie - not that disgusting Christmas pudding stuff. yech!
I'd spend the evening huddled up on the couch between them, listening to music, talking, laughing, playing silly games and getting ever-so-slightly squiffy.
Most of all, throughout the whole day, I would make them feel like they were the the most precious people in the world; the centre of my universe.
Then we'd all doze off in a big sprawly heap on the couch and stay there until Boxing Day morning!