You are fine to get on the train without a reservation, your tickets are sufficient. Swiss trains use a feee seating system, seat reservations are not mandatory, thus optional.
Certain trains, such as the Eurocity to Italy, and panoramic express trains, namely the Glacier Express, the Gotthard Panorama Express, or the GoldenPass Express do require a seat reservation.
If you travel more often, I suggest to buy Junior cards for your kids. The cost is CHF 30 per year/child and entitles free travel while accompanied by a parent holding a valid ticket. You can get the Junior Card at the SBB Travel Center.
Get back to us if you have further queries.