You've all been good, right?
Santa's Elves are watching.
and a more traditional version:
I'm not at home today, I'm spending the afternoon and evening with my niece G and my great nephew E.
E is 2 and 1/4 now, so might be a little more excited about Christmas than he was last year, when to him it was just a day with people visiting to eat dinner and give him things wrapped in bright coloured paper.
It's going to be a lovely day.