Hello Hurrouckie82
Yes, the Swiss Travel Pass is valid on these routes, and I think the Swiss Travel Pass is a good investment.
You only need two adult Saver Day Passes. For the 10 years old, you can request the complimentary Swiss Family Card. With it, your 10 years old cna travel free of charge with you. The 4 years old does not need a ticket at all. In Switzerland, children below 5.99 years oif age travel for free.
Kind regards,
Roland