The best is to book it via SJ or at the ticket window. Have you asked SBB?

For the SJ website, you'll need a pass cover number, which is on the pass cover of a paper pass or which you can request here if you have a mobile pass.

Thanks! yes I tried.  There is a doubt because when I choose the child passenger and I put the age of my child 12 years old, supervise him for the choice of the pass, it disappears?  Why?

there is no Child reduction for Reservations. This means for reservations even a child counts as “adult”.

The Route to Abisko is really scenic :) 

This is a picture from the norwegian site Abisko - Narvik :)