Gold Star family members -- relatives of the 13 American service men and woman killed during withdrawal from the Middle East three years ago -- took the stage and contrasted their interactions with Joe Biden and Donald Trump ... slamming Biden for his administration's response to their killed family.

The major moment kicked off with a video of Biden checking his watch at Andrew's Air Force base after the bodies were returned from Afghanistan ... and, in confessional interviews, they said it seemed like he had better things to do.

Alicia and Herman Lopez -- the parents of Corporal Hunter Lopez who died during the evacuation -- then spoke onstage, adding when the 13 servicemembers' bodies were returned to the U.S.A., Biden met the plane, but they claim he made the moment about himself.

Instead of focusing on their tragedy, they say Biden kept mentioning his son Beau Biden -- who passed from cancer -- and didn't focus on their losses ... a moment of disconnect that's staying with the family members.

Another grievance ... the families criticized Biden for never publicly naming their loved ones and claimed as recently as the debate no one died during the withdrawal -- with Christy Shamblin, mother-in-law to Marine Sgt. Nicole Gee, saying when they met Trump, he knew all their family members' names.

As you may know ... 13 U.S. service members and around 170 Afghanistan civilians were killed at the Kabul Airport by a suicide bomber -- a tragedy the Department of Defense has said wasn’t preventable at a tactical level.

Still, Biden's been criticized for his admin's handling of the situation -- especially the self-imposed August 31 deadline.

The names of all 13 military personnel killed in the incident were read onstage and the family held their pictures too ... with the crowd showing the families a ton of love after they spoke with shouts of "U.S.A." and "Never forget" reverberating throughout the room.