OK. What to do, to make it special for DS?
Obviously all the hype of putting out mince pies & carrots, & drinks!
Read 'The Night before Christmas' at bed time.
Use the Santa Tracker.
Childrens Christmas Carols
Ask him what he'd really really really love for breakfast - get that tomorrow.
Get what you & DH would really like for breakfast.
If you haven't already got him a new outdoor toy, get that tomorrow. A good excuse to play outside & get some fresh air.
Arrange a time to Skype uncle x & grandparents. Maybe during present opening time.
Put their present aside for 'Family Christmas Day' and add bits to the pile, like Christmas crackers & the additional jokes out of the ones you pull.
Acknowledge you can't have another Christmas (Santa only does 1) but you can have a 'Family Christmas' as soon as everyone's well enough!!
Ask DS what things he would like to do to make it extra fun?
Personally I'd make the meal as easy as possible so you can spend more time playing, eating chocolate, watching movies etc.
Make sure any 'no' is a well thought out one, not an automatic one. Have a 'YES' day! Chocolate for breakfast 'yes' play xyz 'yes' campfire in the lounge err 'no'.
Take turns reading a book (if DS hates reading, just you & DH do a chapter each).
5 is a heresy age!
Just make sure he knows that it's ok to be sad that Uncle x can't come, but that you'll see him as soon as you can & have another fun day!!
Decide what you & DH would like to do after DS goes to bed! Film/Game/shag on the sofa with only the Christmas lights on/have a drink & plan things you want to do/achieve next year.
It's disappointing, but throw yourself into it & I'm sure you'll have a great time 🎅🏼