Hello Debrc
If you travel with the Swiss Half Fare Card, you can request the complimentary Swiss Family Card for each child. When doing so, you do not need to purchase tickets for the kids, neither do you have to mention them when purchasing tickets for the adults. It would only be required if you needed seat reservations, for example for panoramic trains (PE).
For your journey, the total amount to be paid is CHF 27.
Kind regards,
Roland
