Christmas/New Year Italy and France Itinerary - all suggestions are appreciated

I would add the Milan days to Florence and fly to Paris from Florence.

Looks way to rushed for me---It kind of takes the fun out of the trip being on such a tight schedule. I know you said your kids are seasoned travelers but this is a burn out pace.

You have 14 nights. My rule is no more than two places to lay my head each week. Pick 4 places and slow the heck down so you can enjoy the trip, Perhaps Rome, Florence, fly to Paris, then London.

So much closes down the 24th-26th you need to carefully consider where you will be for those days and what you will do those days.

• Strasbourg comes recommended on all christmas itineraries
• pl create a backup plans to manage the cases where there may be bad weather, train cancellations etc. for example you may need to skip a city and just go to the next one.
• 2 days in major cities will only give you time to hit 1 or 2 major highlight (or take the hop on hop off). if you try to crunch in more, the whole trip will be a daze and the kids won't be able to distinguish one from the other.
• i feel you are overestimating the time you have in each city - with all the adjustments with packing/unpacking/travel/changing hotel rooms every 1-2 days - it will be a mini amazing race. which is OK - as long as you plan accordingly (hit only the top spots, avoid FOMO, leave spaces for eating leisurely once in a while, missed connections)
  
• if you don' enjoy cold weather (like me), the markets and city centers do get exceedingly cold - get thermal wear or good jackets.

here is another post on Christmas markets - this trip report by Pat gave a comparison of Strasbourg with others. https://community.ricksteves.com/travel-forum/trip-reports/christmas-markets-switzerland-france-germany-2019

Have you already booked the flights? If not, maybe skip London and fly out of Paris?
If already booked, I’d cut Milan unless there’s something there your kids are dying to do. Lake District may not be great in winter and not sure Last Supper is worth it for that age (due to the additional travel factor).
Any overnight trains you can take instead of intra-Europe flights? Trains are generally more reliable and kids love the idea of sleeping on a train. Our last trip was greatly altered by a very delayed EasyJet flight from Barcelona to Geneva, causing us to miss “doing” Bern entirely.
(I have a 12-yo and a 15-yo, both experienced travelers, and your schedule pace scares me, esp going without another adult to help you. You’re solely responsible for everything on this trip - all navigation, all finding the hotels, etc and that can get very mentally exhausting, esp if the kids break down on you).
Also as others have noted Europe closes down WAY MORE on Dec 24-26 than we are used to here in the states.
Edited to add: there is a direct flight from Florence to Strasbourg.

Traveling over Christmas and New Years presents more things being closed, including closed down transportation.
Have you checked to see what will be closed due to the holidays? We were in London for Christmas, New Year’s in Rome. A lot was closed, restaurants, museums, buses, subways. I would not travel over the holidays again. A friend in London helped a lot, finding places open to eat, etc.
Your itinerary is exhausting! Cut some places from it, stay longer in those remaining. Check for closures in each place and then make plans. This includes meals on Christmas Eve, Christmas Day. Hotels will still serve meals.

Sorry but my head is spinning just reading your itinerary. Way too much traveling, way too many cities. I think you and your family will have a much better time if you slow down and keep it to three or maybe four stops max. Save France (or Italy) for another trip.

Not where you thought you would be, but London transportation-tube, etc. DOES NOT operate 25DEC. The service that evening at St. Paul’s, however, is wonderful. This was in early 2000’s, so may have changed.

Also wonder if flying into Basel and then train to Strasbourg might be an option.
You can fly from Florence to Strasbourg. At least according to rome2rio!

Thanks all for your kind words/concerns and suggestions!

I posted a reply earlier with more questions but not sure why I can't see it anymore. Any one knows why? Thanks!