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Yes, the Children’s Day Pass is the best ticket for a child if the half fare point-to-point ticket costs more than CHF 19.
Whether you should purchase a Children’s Day Pass is difficult to say, as it all depends on your travel plans. If you plan to do multiple journeys, the Swiss Half Fare Card would be beneficial for you. And it comes with the complimentary Swiss Family Card that entitles your child to travel free of charge when accompanied by you and while you hold a valid ticket.
Swiss Half Fare Card – Switzerland at half the price | SBB
Swiss Family Card | Switzerland Tourism (myswitzerland.com)
If you are not into the Swiss Half Fare Card, you could still buy the Junior Card at any staffed ticket counter. The Junior Card costs CHF 30, is valid one year, and offers the same advantages as the Swiss Family Card.