If you buy the Half Fare Card (the 120 CHF one for tourists, not the other one for residents) it comes with the Free Family Pass, which gives free travel to your children, provided the parents have tickets.,
So when purchasing the HFC add your children to the order, and tick the check box indicating that you intend them always to be accompanied.
So then you only need tickets for the adults, so proceed with buying the Saver Day Pass for you and your wife. You can always buy the HFC (for you, wife and child) later, and can even do that at the station once you are here.
And with the Family Card mountain excursions like the Titlis etc… are indeed free for the kids. But you might have to get to the ticket office first to get the “free” ticket, as cable cars often have turnstiles.