Hello traveling
Welcome to the SBB Community.
Kindly note, there is no ticket offer named ‘Family Pass’.
You probably purchased the Swiss Travel Pass that can be purchased by any individual, and not just by families. Since you do have children, you have got, in addition, the complimentary Swiss Family Card.
Assuming the above tickets you are all set for now and can right use the Swiss Travel Pass from its first day of validity by hopping on and off Swiss transit services at will.
There is no need to make reservations, except for some PE services such as the Glacier Express.
Please read our blog for completing your knowledge about the use of trains in Switzerland:
https://community.sbb.ch/blog/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
Kind regards,
Roland