Traveling by train from paris to venice with overnight stop on switzerland

There are no direct route trains Paris to Venice that pass through or stop near a picturesque town in Switzerland.
You could just book Paris to Milan and then go North to Lugano Switzerland. It will be separate tickets

This isn't really feasible. There aren't any trains that will go directly from Paris to Venice with the opportunity to just hop off in the mountains of Switzerland for the night.
To get into the Swiss mountains there really isn't any direct route. It's going to be, at the very least, a flight and a train ride to get in, and a 2-3 stop train ride to get out of the mountains and down to Venice.
That said, you can take a direct train from Paris to Zurich, take a train up into the mountains for a night or two, and then train from Zurich to Venice with one change.
To play around with possibilities you may want to use the website rome2rio.com. It will show you all of the possible ways to get from point A to point B anywhere in the world.

Hi,

There is a night train going to Venice. It departs from Munich, a hub for night nights going south to Italy, east to Budapest, and north to Hamburg. Since I travel solo, I would do this option:

Take the Paris to Frankfurt Hbf. early morning TGV train, arrives ca 11 am, have a leisurely lunch at Frankfurt Hbf, then take Frankfurt to Munich Hbf on the iCE, where you have a few hours to relax and see the Zentrum before getting in time for the night train Munich Hbf to Venice.

With a family of five, this option could be far more taxing. Traveling solo I would have no problems taking this route going from Paris to Venice but then it's without a stopover.

Given the choice of having to change trains, here twice (Frankfurt and Munich), I would rather do that in Germany.

Here is The Man in Seat 61's suggestion:

https://www.seat61.com/BerninaExpress.htm#Bernina_Express_to_go_from_London,_Paris_or_Zurich_to_Italy

Be sure to see the tip about how to buy the Bernina Express ticket cheaply. I did, and it worked.

We traveled from Zurich to Venice on the Bernina Pass route as suggested above ( Man in Seat 61). We stayed overnight in Samedan in Switzerland and Varenna in Italy.

However, this would not be any easier than the Kandersteg route. That one need not be so difficult. Train from Paris to Basel, then Basel to Spiez, then Spiez to Kandersteg. Next day, Kandersteg to Brig, Brig to Milan, and Milan to Venice.

Any route you take through Switzerland is going to involve changes, but it is not difficult once you learn to read the train schedules. The easiest one to use for schedules for multi-country travel is the German site bahn.de
You cannot buy the tickets there, but you can see the route and times. Then go to Trainline.eu and SBB.ch to buy the tickets for the discounted advance fares ( available in France and Italy but not Switzerland).

As said above, there is no direct route by train, but there is one fun one I can suggest with a minimum of changes.

The family might consider a night (or 3) in Luzern (local spelling, you may know it as Lucerne).

Paris > Basel; Basel > Luzern; Luzern (probably via Arth-Goldau) > Milano (local spelling, you may know it as Milan); Milano > Venezia Santa Lucia (local spelling, with the Venice station which is on the Grand Canal).

So just 1 high speed TGV train to Basel, then an easy connection at Basel SBB to the short train to Luzern.

A night with views of the magnificent Lake Lucerne (Vierwaldstaettersee in German), the boats, the ancient covered bridge (rebuilt after a fire) and the views of the surrounding mountains. Maybe if you have time, a ride on a boat or a ride up a mountain.

Then a simple train (perhaps with the Arth-Goldau change) ride to Milano, and an easy change to a high speed train to Venice. Make sure to get off at Venezia Santa Lucia and not at Venezia Mestre.