Here is a calendar from timeanddate.com, showing Paris weather in the first week of March 2021. Clicking on the big arrow at the right end gets you the next week. Just above the calendar, on the right, is a "Select Month" menu, which you can use to get weather for March 2020, 2019, etc. for about ten years back. That should give you a sense of what to expect next March, with the usual caveats about weather prediction. (I learned about this site from acraven, one of the most helpful and conscientious posters here, just can't believe she hasn't already pointed you to it.)
My own late-March visit to Paris about ten years ago was on the chilly and wet side, but nothing extreme. It probably won't be too cold to enjoy if you bring an extra layer and something waterproof for each traveler. The old saying is that there's no bad weather, only wrong clothing. Stay flexible about indoor vs. outdoor activities, keeping in mind that the youngest one isn't likely to want to spend lots of time in museums. ;-)