I realized you cannot buy a train ticket for a child if the discount option Junior TravelCard is selected. At the checkout stage, it will highlight “Children with the Junior Travelcard accompanied by a parent travel free and do not require a ticket.”
So, we only need to purchase train tickets for Adults? In addition, there is no seat reservations required for inter-city trains? I am traveling around Zurich, Spiez, Zermatt, etc, with the inter-city trains, not any of the Express trains like Glacier Express.