I'm so sorry, but there is no way round how flat you will feel on Christmas day. But you can limit the damage (as it were). Have some food you truly enjoy waiting ready when you get home, and some things that will make you feel good, be that new candles and bath stuff, a new movie and chocs, wine, you get my drift. This is the time you can treat yourself, and be very very kind and gentle to yourself.
When do the dc go? Can you do a Christmas Eve type thing with them? Jammies, snacks, movie, a little special 'early' pressie just from Mummy, rather than the Boxing Day of overtired overexcited overchristmas dc?
Will there be others in at work? Can you take posh nibbly things and have a nice time despite things?
As my dc got older, they really needed to see me open something, they do suddenly become aware of it (youngest was about 3.5 but the others always made me things off their own bats, but I very luckily have most excellent parents). So I now buy 4 little bits of nothing for me (and dp...it does get better, promise) so I can open something from each child.
it's a bit shit, but things do get easier, until then, look after yourself too x.