It is up to you to know how many pass days you might need. As Swiss tickets are very expensive it might be a good idea to use a pass day depending on your journey. The 11 y.o. child travels for free but you need to book a free pass + pay seat reservations for them too.
Seat reservations to add (per person) :
- 13€ Rome - Florence
- 13€ Florence - Milan
- 26 CHF for the Bernina Express : the route can be done on hourly reservation-free regional trains (some with 2 open-air coaches in summer, AW symbol on SBB app)
- 49 CHF for the Glacier Express to Brig (very popular, full weeks in advance) but the route can be done on hourly regional trains : St. Moritz - Reichenau-Tamins (or Chur) - Disentis/Mustér - Andermatt - Brig*. Not longer, less crowded and fully reservation-free.
- 9.80€ (for the whole family) Interlaken - Ulm through bahn.com
- 17€ Frankfurt - Paris
- 30€ Paris - London. Book ASAP (limited number of seats)
- 30€ London - Brussels. Book ASAP
- Brussels - Amsterdam use the hourly reservation-free IC train instead of the 27€ Thalys.
- 3€ Amsterdam - Frankfurt. Book well in advance too (very popular route).
For Italy + Amsterdam - Frankfurt use : tickets.oebb.at (no booking fee) -> add Eurail as a discount and select one-way tickets.
Eurostar use : https://www.b-europe.com/EN/Booking/Pass#TravelWish
About Interlaken area : Eurail pass fully valid on boats on Lake Thun and Brienz. 25% discount for tickets to Lauterbrunnen, Grindelwald and above
*another very scenic route to Interlaken (I'd choose this one) : St. Moritz - ... - Andermatt - Göschenen - (every other hour, change in Arth-Goldau) - Lucerne - Interlaken Ost
