Agree with what the majority have said here and postpone this trip for now. As for UK based alternatives while nothing is going to live up to the magic of Disney their are nice Winter / Christmas themed attractions. No idea where your based but in Yorkshire there's Stockeld Park which has Nordic Skiing, Ice Skating, Woodland Walk, Maze Illuminations, usually a Grotto. It can be quite pricey http://www.stockeldpark.co.uk/activities/season/christmas/ If you were doing an overnight stay and the kids are into Harry Potter you could also go to York were the Shambles Street is very much like Harry Potter's Diagon Alley with shops selling potions and merch. https://www.visityork.org/explore/shambles-p799721 York also has a new wizard golf course Hole in Wand https://theholeinwand.com/
I was at disneyland paris two christmas' ago, it was so cold and slippy. It wasnt as big as disneyland near LA, like two rides broke in a row after getting to the very front of the queue. If i had gone to paris first it would have totally put me off disneyland forever but i had gone to the LA one a few months before it and i literally cried it was that magical (lol) ive seen florida is supposed to be even bigger (cheeky)
There are definitely things OP will need to know before hand (if you don't know about boarding passes for Rise of the Resistance, you won't be able to ride it) and other things like Memory Maker (free ride photos that you can download when you get home). Be careful not to spoil yourself by watching PoV ride videos though. They're never as impressive recorded on a GoPro and you'll spoil the surprise. Only use them if you're unsure if someone will be able to handle the ride.
We went to Florida 10 years ago for our Honeymoon and have been to Paris twice with our three kids since, once a couple of years ago over Christmas. To be completely honest Paris is nothing compared to Florida. Broad generalisations but the American customer service is generally top notch, even better at Disney. The French are not renowned for their customer service and this is what we experienced at Disney. Some of the cast members were nice don’t get me wrong, but not a patch on Florida. Christmas in Paris was completely manic (we went Christmas Eve for 3 nights and stayed at Davy Crockett), it was absolutely exhausting but the kids loved it and we have loads of great memories. We liked Davy Crockett as it’s away from the hustle and bustle (a short drive to the park) but as it’s still a Disney hotel you still get the extra magic time in the morning and don’t have to pay for parking. Obviously it’s all a bit different now but we found the visitors in Paris generally extremely rude and out for themselves. They will physically push you out the way if you’re in their path and trying to get a decent view for the fireworks was like a wrestling match. We queued for 2 hours to meet Mickey on Christmas Day and I swear I’m not exaggerating when I say there was an actual fist fight between two French families when one accused the other of pushing in front of them in the queue! To summarise our thoughts- Disneyland Paris is good, Disneyworld Florida is ‘magical’.
If you save for Florida you will NOT regret it. It's amazing! However I will say do your research first, watch vlogs on Youtube, learn how to use the fastpass system when it's put back in to place etc. It will save a LOT of time/money when you get there.