Hi emmadeujfalussy
In order to answer your question we are in need of more information from you. Could you tell us the start as well as the end destination of his journey?
As a general saying: provided your son’s age is between 6 and 15.99 years, he could just buy a return ticket at half fare. If the ticket cost is higher than CHF 19 for the return ticket, there is the Children day pass for CHF 19 per day. It is good to travel with buses and trains. Day Pass Children | SBB
Or, if he travels in the evening only, there is the seven25 Abo. Depending where you live, there might be other ticket offers from the local fare network.
If you do not want to share the journey information with us, for example for privacy concerns, which would be ok, please get in touch with the SBB Contact Center Tel. [0848 44 66 88](tel:0848 44 66 88) CHF 0.08/min or visit any of the staffed travel centres.
Best regards,
Roland