Also, to answer your question on the other thread about using a Swiss Pass on the trip from Luzern to Paris:
You will change trains in Basel and catch the direct train to Paris. Your pass will take you as far as Basel, but you must have a ticket from there to Paris. You can save a lot by buying this about 3 months in advance. You can buy onnthe Swiss train site SBB.ch and it will figure in your Pass discount. Choose "GA 2.cl" for yourself from the drop-down menu where it asks for a pass, and "Junior Card" for your son. If you have a Half-Fare Card instead, there is a choice for that as well. Your son will still be free with the Family Card.
I just checked a random date 3 months away ( June4) and here are the prices I found for one adult:
Normal price for Basel to Paris, 199 CHF
"Special offer" price either 42 or 49 CHF, depending on the degree of flexibility you prefer.
As you can see, this is quite a saving and well worth the effort of booking in advance; just remember the tix are non-refundable and good only on the train you book.
You could also just book Basel to Paris ( leaving out the Luzern leg), and use your passes to get to Basel, but I found the Special Offer prices to be higher that way (66-73 CHF).
You can check trainline.eu as well to see if there are better prices, or if you have trouble with your credit card on SBB.ch
https://www.thetrainline.com/?redirected=true
Some people have reported problems with their American Visa cards on various European train websites. American Express seems to work fine, at least for me on all the different train sites so far.