No. A Saver Day Pass that was purchased for 3rd August is only valid until 4th August 05:00 AM. The Saver Day Pass is not valid for a train to Milan. For this train, you would have to buy an Eurocity-Ticket from either www.sbb.ch/en or www.trenitalia.com/en.html. With this ticket, the seat reservations are automatically issued upon ticket purchase.
For Zurich, and depending on where you stay, you could buy a ZVV Day Pass at full fare (1/1) for the parents and half fare (½) for the children aged 6 to 15.99 years of age; below, children travel for free: 24h-tickets of the Zürcher Verkehrsverbund – ZVV.