Of course I familiarized with link you mentioned. It is just not obvious if this part concerns children. According to rules, holders of STS are free of charge in mountain excursions, I am aware of it. Children travel for free with their parents holding STS, I am aware of this rule as well. I was not sure if children take advantage of ALL benefits for free (i. e. mountain excursions or museums), not only transport.
In this case, STS is even better for us than I thought, I'm going to buy STS for me and my wife, Swiss Family Card for children and we will be able to enjoy all available attractions for free 🙂
Have a nice day,