Ticket and seat reservation Jungfrau trip

we are family of 4 which includes one 10 year old kid. we have already purchased swiss travel pass and would be staying in interlaken. we want to travel to jungfraujoch from interlaken while going up via grindelwad and coming down wengen. I need to know at which point will i have to buy train ticket as i heard jungfraujoch journey is only 25% discounted on swiss travel pass. Also do i need seat reservations for any leg of this journey? Does my child also get only 25% discount or is it free for her?

Thanks for your first post here yprad78!

The leg Grindelwald - Jungfraujoch - Wengen is discounted by 25%. The remainder of the trip is free (see the map please). You can buy the ticket in Interlaken. The child travels for free, without a ticket, if you have a Swiss Family Card.

Seat reservations are optional: myswissalps.com/ jungfraujoch/tickets.

Have fun!