Hello Mandriel
It would be a good idea to buy Half Fare Cards because your kids will travel free of charge with the included Family Card. Don’t forget to add their names when you order the cards (only for the 2 kids aged 9 and 6).
Otherwise, you can find the prices for the two adults with Half Fare for every journey by searching the timetables. You may have following discounts:
Supersaver Tickets: You can travel only with the selected trains, not refundable
Supersaver Tickets Flex: You can travel only with the selected trains, 75% refundable before departure
Saver Day Pass: Full flexibility, not refundable
Point-to-point Tickets: valid for one journey between the two stations with every train, refundable until the day before departure. It is not necessary to buy such tickets in advance, the price is always the same.
Don’t buy Supersaver Tickets from the airport, only point-to-point tickets (I don’t think that Saver Day Passes are cheaper). Supersaver Tickets would be no more valid if your flight is delayed.
Half Fare and Family Cards are not valid in Italy, you have to buy regular tickets. If you travel with a regional train RE80, you can buy tickets Spurga - Milano for the adults, with Half Fare in Switzerland, and Chiasso - Milano for the kids. Note that these tickets are only valid for 4 hours.
Kind regards
Danhiel