Hi, you haven't said if you have kids or what age but I personally wouldn't recommend a day trip to Paris centre if you've got really little ones at Christmas.
I'm a big fan of Paris having been loads before kids, we took them last December for a day trip from DLRP and it was horrendous. I've bulleted why as there are so many reasons.
- Amazingly busy
- Very very cold (colder than DLRP I think)
- A LOT of walking, I mean a LOT
- Nowhere near enough lifts for pushchairs
- People of all nationalities seemed very unprepared to allow pushchairs through
- We got stuck in the underground during a bomb-scare/train derailment which while I grant you is unlikely to happen to you it highlights the fact that there are very few lifts. I had to carry two kids and a pushchair up numerous flights of stairs while my wife carried the bags while men with guns pushed us over repeatedly
- Very little to do for kids except the sights and the Eiffel tower can be a very long queue
Sorry for the downsides but I just think young families are better staying at the resort.