Apr 29, 2018 - 1:25 PM
in reply to Raj
Hi Raj, and welcome to MySwissAlps!
A child entitled to free travel doesn't need any sort of ticket. Just show your Swiss Family Card when asked.
The Jungfrau website isn't particularly clear on this point, but if you download the current timetable from the following page, and read the first page under the heading Buy tickets online at jungfrau.ch/shop, it says: Swiss Family Card valid.
However, it's definitely not a good idea to buy your ticket more than 24-48 hours in advance. If it turns out that the weather is not suitable, or the Jungfraujoch is in the clouds, you will not see anything and cannot get a refund on your ticket or exchange it for another day.
What time of year are you travelling?