Hello Yievaunnigh33
You could have got it together with your Swiss Half Fare Card. When entering the passengers for the Swiss Half Fare Card, you could also have entered your kids and got the Swiss Family Card in a one stop shopping.
Now, you cannot request it online anymore but must see an SBB travel center here in Switzerland to get a paper copy of it. It is advisable that you see the travel center at the airport should you arrive by air.
Your tickets always require your physical passport (no copies / no photos of it on smart phones).
Kind regards,
Roland