So I've found a link on the adult PNR called "Link Reservation" but that seems to require an already made reservation.

When I go to make a reservation, clicking through from Google Flights and entering the child's details, I get this message:
"To book children aged 18 and under who are traveling alone, select 0 adults and the number of children. Search for flights."

When I search for flights from the Alaska AIrlines website homepage as they suggest, I then get a screen which only gives options for unaccompanied minors.

I'd be happy to book the ticket like that and then link them, but I don't want it to have an "unaccompanied minor" flag on it which might cause inconvenience and waste time at the airport.

Is this perhaps something to do with the new vs. old flight search format, as described here:

https://www.flyertalk.com/forum/alas...ht-search.html

Is there a way to force the old flight search version, if the feature I'm looking for was there and isn't in the new search design?