planning a 10 days trip to Europe (Germany, France ,Italy and Switzerland) from Mumbai

YES, you are trying to do too much.
You have one day in Paris, three days in Italy to see Rome, Venice, Siena, Milan, Tuscany. NO WAY can you visit all those places, unless you just drive through.

A good plan for visiting Rome, Florence and Venice is for 10-14 days.

Use TripAdvisor, put in the name of the city you are visiting and all Things To Do. It will give you many items of interest. Also, that won't cover it all.

Cut back on your itinerary significantly. Pick ONE or perhaps two countries and spend at least 3-4 days in cities like Paris and Rome.

I don't think your Italy itinerary is physically possible, unless you simply ride by these destinations on the train and don't get out. 10 days is too short of a time even to see all the places you list in Italy.

Your first and last days in Europe will be just getting to and from the airport and getting over jet lag. Every time you move destinations even within countries, you will lose at least half a day door to door, so I would suggest that you focus on Switzerland if that is of most interest to you plus either Paris (5 days would be a rushed visit) or Italy - say Rome plus Venice. Anything else will be very rushed and you will spend longer in transit than actually seeing places.

I agree this is a crazy itinerary, moreso with a child. My advice is to select two places to visit and save the remainder for another time.
5 nights in Paris and then 5 nights in Rome would be very nice.

I think the OP must be pulling our leg. Surely no one could think that that itinerary is even physically possible. OP, get real, pick one country. Given your preferences

"We like scenic places, mountains and beaches, and aren't very big on museums and forts.'

I'd recommend just sticking with Switzerland and possibly a bit of Bavaria.

I'd recommend just sticking with Switzerland and possibly a bit of
Bavaria.

Realistically, Switzerland is just a big fort and the OP is not interested in forts.

I'm with CJean, I think the OP is pulling our collective legs. If not, the only thing I could say is it might work if teleportation was a real thing, otherwise it's unlikely that it's even physically or logistically possible.

Skip Italy and Paris (Why bother with Paris with only one day?) Join a bus tour to Switzerland and Germany.

An interesting exercise to plan a trip like this, especially by train . . . Day 1: arrive Paris, take taxi to train station. Have driver go past Eiffel Tower and Arc de Triomphe so you can see Paris. Take train to Rome. Not as many overnight trains as there used to be, so this will take a while, you'll spend tonight on the train or in train stations. Day 2: Arrive Rome, probably late in the day. Take Rick's recommended Rome night walk, have dinner. Stay here (as in all destinations) in a hotel as near station as possible (sorry, no time to find Air B&Bs on this trip). Day 3: Early train to Florence. See Michelangelo's David (just one statue so it won't take long but you may need advance ticket), and look up at Duomo. Back to station, bus to Siena. Stay there tonight. Day 4: Bus to Florence, train to Venice, arrive about midday. Walk to St. Mark's Square over Rialto Bridge and back. You've seen Venice. Late train to Milan. If you have time take subway to Duomo stop and look at outside. If not, do that first thing on Day 5: Train to Cologne. This will take most of the day. Luckily Cologne's major sight, the Cathedral, is right next to the station. And it's only about a 10 minute walk to the banks of the Rhine -- not the most scenic Rhine, true, but you can see more Rhine out the train window as you head for Heidelberg. Stay there tonight, see the town this evening. Day 6: Trains to Rothenburg and on to Munich. You may have to change trains a few times as Rothenburg is a small place, but that means you can see it in an hour or so. Arrive late in Munich, walk to Hofbrauhaus and have a well earned large beer or two. Day 7: Good news, you can fit Austria into this itinerary too. Train to Vienna. Arrive in the afternoon, see that big Ferris wheel and have a wiener schnitzel. Day 8: Early train to Salzburg, a Sound of Music day tour, continue on to Zurich, arrive late. Day 9: You get to ride the train! You're on schedule to take the scenic Swiss train rides today. Day 10: Leave for home relaxed and rested from your European holiday. If you want to go to the beach you can tighten this schedule some more (such as no Austria) and take a beach day in Venice (Lido) or near Rome, neither are great beaches but they'll do in a pinch.
OK, in all seriousness, I think you can see from this that the other advice to focus your trip on a few places (like just Italy) is good.

Please see the three different 13- or 14-day "Best of Europe" and "Family Europe" tour itinerary plans at https://www.ricksteves.com/tours/europe. Any of them makes a good starting plan for you, but still requires cuts. You'll see that:

• They take a bit longer than the time you have and cover fewer destinations than you've listed.
• Many people would take these routes slower but basically nobody would take them faster.
• Where Rick's tour may "officially" spend only two nights in a starting city like Paris, many tour members arrive early to give it more time on their own.
• Part of what makes the tour timing work is having a dedicated tour bus. There are areas where trains can be faster than tour buses, but that's generally to connect major cities within one country (like Venice-Florence-Rome) and not when connecting small towns on small, regional and mountain train lines.

Rick’s Train Travel Time & cost Map gives you a quick overview of faster train travel times in hours, as well as regular (full-price) 2nd-class fares. But since it's focused on big cities, it doesn't reflect the additional time to further connect to small towns.

For actual train connection timing between any two towns on your list, Looking Up Train Schedules and Routes Online gives you the Deutsche Bahn train schedule link and tips for using it.