Hi - we are traveling to nice to see French Riviera day 1 (feb26) and plan to depart nice on morning mar 2nd. We leave for the states from Milan on following Sunday March 8 at 9 am. Had planned to see Venice for sure but read don’t need a lot of time in Milan. Really interested to see if we could see Swiss alps for a couple of days before going to Venice. Maybe do a train like Bernini express - could spend a day or 2 in Swiss.
Another alternate is to see Florence. Fly of 4 with 2 teenage boys. Looking at train travel.
I haven't been to Switzerland (yet) so I can't give you any specific advice there, but I strongly recommend asking the boys to help with the planning. When my sons were young the adults planned the general outlines (towns, hotels) and let them help fill the days. We rented a rowboat on Loch Awe, sawo a video game parlor in Japan, and took a walking food tour of Amsterdam.
As an option. Consider a loop through the Dolomites, starting at Verona and coming back down into Venice, might be a good way to incorporate mountains without losing too much time to travel.
EasyJet flies nonstop from Nice to Geneve at 7:00 a.m. or Nice to Basel at 8:45 for about $40 per person (with advance booking). Other flights are in the evening. (Only Swiss Air flies from Nice to Zurich, so that route is more expensive.) You'd still need to take a train to a sightseeing base within Switzerland, but that one flight would save about 8 hours of train time to cross France.
The best train schedule from Luzern (for instance) to Venice takes 6.5 hours with a connection at Arth-Goldau. The Bernina Express is a detour that takes much longer.
Looking Up Train Schedules and Routes Online gives you the Deutsche Bahn train schedule link and tips for using it.
Will you have a rental car, or use public transportation? A car would be useful if you want to spend most of your time touring the alps. For example, you could pick up your rental car in Nice and turn it in when you arrive in Venice, then take a train from Milan back to Venice on Saturday afternoon.
There will likely be a "one-way" surcharge for turning it in in a different country. Europcar seems to recognize that this is a popular wish of travelers
https://www.europcar.com/location/one-way-car-rental
You could avoid the charge by taking public transportation from Nice into Italy, either San Remo or (if you need a bigger rental car depot with more options) Turn, Milan, or Genoa.
Be aware that in early March you could be dealing with snowstorms in the alps. If you have a rental car you can adjust your route according to the weather forecast.