Switzerland to Paris

Hello here are answers to your questions

I see a direct train from Lausanne to Paris. It is labelled TGV: A. Do kids also travel free on these trains like in the Swiss trains with a paying adult? Kids aged 2 and 7 if it makes a difference

Kids 0-4 are free on TGV Children between the ages of 4 and 12 travel at half the adult fare, subject to availability.

B. Does Swiss half-fare card get any discount on this train? For some reason SBB website is not showing any price. A 3rd party lists the price as $168 (pretty steep compared to Swiss trains of the same 4hr duration!)

The TGV is a train operated by France SNCF; the Swiss Half Fare card does not cover TGV trains. The price is steep because you are researching not far enough in advance. The prices go up as capacity decreases.

Are there any "overnight" trains between Paris & Lausanne/Interlaken/Bern. Overnight = get in at ~10PM, sleep and get out early morning?

No

Any Eurorail pass that is approximately in the same price range as Swiss half fare and gets discounts on both Swiss trains and the train to Pai

I doubt it but someone may chime in or you could go to Eurail site and research this

Thanks Jazz+Travels. Very helpful.

Do you know if the TGVs are refundable? Thinking of booking them before they go even higher, and cancel if needed based on weather in Switzerland.

Found my answer. Looks like there is 30 Euro cancellation fee if you get the standard tickets. Looks like backup plans are expensive!

I am asking Swiss government for a rebate (or a free Rolex watch) if the rain spoils my vacation!

It sounds like an expensive plan B... If you really need a plan B, I would look at the southern side of the Alps, like Lugano, Locarno, Stresa or Como - the weather could be very different, and your halffare cards would take you all the way or most of the way.
But I just checked this week's forecast and mostly see afternoon showers/rainstorms, which is quite common in mountain areas later in the summer. I wouldn't worry.

Instead of going all the way to Paris, consider Dijon, a smallish medieval city that is on the way from western Switzerland to Paris. Or head north instead of west and try Strasbourg.

Thanks for the tips @Dijon and @balso. Yes, Lugano and Pontresina are also on my list but they also seemed to be hit by rain. @balso are you saying that even on these rainy days, the AM is usually good (also are the rains super short and things become visible soon after)?

I will be flying out of Milan. So, I am keeping latter part of the trip in Pontresina/Lugano cancellable and heading down to the Italian riviera if things continue to look gloomy. Maybe just rent a car and drive from Nice to Cinque Terre and head back. Any suggestions in that area?

I don't see much gloom in the forecast, thankfully for you. Just showers.
I was just staying, that unsettled afternoons are quite commonplace in our mountains in August-September, so if the forecast says thunderstorms you're probably good in the mornings. But frankly that's guesswork, you'll see once you're there and I'm sure you'll have a great time! You'll see how green the landscape is, and if it rains you'll understand why it's green :-)

@balso looks like we have family in Paris making it cost even. So, seriously thinking about option B. Worst case we lose 120 euro in cancellation fees (seems like good travel insurance!)

One Quick Q: Paris to Milan overnight train says compartment with 6 couchettes. Are these the compartments with sleeping berths?

Could you be overthinking this? Why not just enjoy Switzerland as you set out to do? We are not talking grey days with non-stop rain. Showers, brief storms, but still plenty of opportunities to get out and enjoy.

Forecast for Interlaken is now dry until Sunday, perhaps even next Tuesday... fine weather in my book, not too hot.
https://www.meteosuisse.admin.ch/home.html?tab=overview&date=6days
Relax and enjoy Switzerland :-)

For completeness' sake, regarding your question on the overnight train: yes, "couchette" means berth, so you're looking at a compartment with 6 berths. The Paris-Milan-Venice overnight train is quite basic and worn, cheap fares must come with low expectations.

Thanks @balso. Yes, definitely keeping Paris as backup. Ideally, would like to dedicate full 2 weeks to country.

Our first full day in Jungfrau is Tuesday. Zermatt Fri/Sat. Fingers crossed. I should you pay you to check the weather since it seems to be good news when you check! :)