How about one of [[http://www.hobbycraft.co.uk/wall-hanging-felt-christmas-tree-90cm/609008-1000 these felt christmas tree] wall hangings from Hobbycraft?
They're only £6 and there's money off if you join their free club too.
You could put it up at home and then take it with you - would give some continuity for this year and wouldn't take up much space.
Any special christmas dvds that you usually watch that you can take with you? If you take several you can take them in a little holder rather than take them in their boxes to take up less space.
I can highly recommend the Tom and Jerry A Nutcracker's Tale (it's usually about £3 on Amazon) - my dc have been watching it since they were tiny and now at 11 and 8 they still love it at Christmas. It's the nutcracker ballet music with the story retold in inimitable T&J style so it's not a really annoying kiddie style film soundtrack. And lots of it is very very funny, there's very little spoken language so great if different people have different languages.
Can you make sure that you have small portable advent calendars to take with you?
Can you write special letters to Santa (for the youngest) to explain that you will be somewhere different and flying home on the plane so if he does have any big presents then please can he leave them for you at home but you will have your stocking with you so please could you have that in France. And maybe spend some time looking at french xmas traditions with your eldest to find one that sounds a really nice idea (having checked with your friends that it's possible!) so that there's one thing that she is looking forward to.
My local Sainsburys had some lovely little coloured kilner bottles that would have been great for home made plum vodka etc - but would you be allowed to take that on planes? Or can you only take booze that has has been bottled and labelled properly to show alcohol percentage etc?
Also big up the 'second christmas' when you get home - get the dc involved in deciding exactly when you will have it when you get home (as soon as you walk through the door, the next day, two days later, new year's day etc) so that there's a definite plan and there won't be worries about favourite bits of the usual traditional christmas going missing.
And if you do get your dd a phone, do check out what will happen if she switches it on for the first time in France - you don't want to find out that it has decided it's a french phone that you get charged to unlock from a french network! Or that you end up spending £££ because it downloads everything it needs to set up using roaming data or whatever. Might be worth seeing if you need to set it up in advance and have a cheap local data card (or check if your hosts have wifi that they don't mind her using) as she might be upset if she gets a phone and then can't do anything with it because she's in France!
Also check out the Christmas Bargain threads in the Christmas section - there are some great ideas on there for all sorts of presents, including portable ones. If your youngest is old enough for playmobil, you can often get it cheaper online from amazon.de rather than the UK amazon for example, even including postage from germany to the uk so guess it would be even better value in France, if your hosts are happy to receive parcels for you.
Hope you all have a fab Christmas break 