Originally Posted by
Smaug
If you have the regular Amex Platinum card (NOT the Delta Platinum card), then the two adults will have access. There will be a guest fee of $39 for the child.
Since you are traveling on a domestic itinerary, the Elite Plus benefit does not apply.
In the event you are referring to the Delta Platinum card, then there would be a cost of $117 ($39 fee x 3 people).
This. If the airline you've selected for your AMEX Plat airline credit is "Delta" and you haven't used it up for this year, the $39 fee can go against your $200 credit.
You will have to pay again on arrival AFAIK -- I believe DL has done away with "day passes" that are transferrable throughout the itinerary though I could be wrong on that (last time I got one when traveling with my wife, they stamped it at ATL and I recall it indicating it was for use at ATL lounges only but YMMV)