Hi ilyanim
I am uncertain if I understood your question correctly.
Yes, for the child 9 YRS you can buy a Child Day Pass at CHF 19. The other child does not need a ticket.
Where did you try to buy your ticket? With the SBB Mobile app or with the sbb.ch ticket shop? The total amount should be at CHF 123.
We gladly assist you further; to do so, please provide additional information.
Best regards,
Roland