Hello Mueteequu68
The Swiss Family Card is only available if you (as parent) purchase in addition the Swiss Half Fare Card, or the Swiss Travel Pass. In a nutshell, the Swiss Travel System products for tourists.
https://www.sbb.ch/en/tickets-offers/tickets/guests-abroad/swiss-halffare-card.html
If you don’t, you could purchase the Junior Card for your child. It costs CHF 30 per child and year and offers the same benefits as the Swiss Family Card. The Junior Card for tourists is a paper ticket that is available from any railway travel center in Switzerland.
Please keep in mind that your Saver Day Pass is only valid together with your physical passport or national ID card.
Kind regards,
Roland