Luke's mother, Heather, remained in critical condition on Monday.
A family member said the rest of the injured Bresette family is expected to recover just fine.
Sam Bresette, 8, has a broken leg and nose. Tyler Bresette, 5, suffered a concussion.
As of Monday morning, friends said Heather Bresette, who had undergone surgery and remained unconscious through the weekend, still had not learned the accident had killed her son Luke.
An airport spokeswoman had said the new terminal where the accident occurred had just opened last week after a $201 million effort.
One witness account to Alabama media said the airport sign appeared only to have been loosely attached, with what looked like "liquid nails".
An investigation is underway.
Counselors encouraged Luke's classmates to either discuss their thoughts in class on Monday about losing a classmate or draw out their feelings.
Fellow St. Thomas More students wrote on one poster that hung in the hall:
'You will always be in our hearts' and 'Coolist Person I Know.'
Friends knew Luke loved and played sports. Another poster read, "KU won because of you."
Luke's uncle, Alex Bresette, said the family is devastated about the child's sudden death.
"I just encourage everybody to keep praying, and hug and kiss their loved ones a little bit more," he said.
The Bresette family was returning home from a spring break vacation in Destin, Fla., when the fatal tragedy occurred.
No funeral arrangements have been made.
St. Thomas More School has set up the Luke Bresette Fund. You can give online at www.stmkc.com or send a check directly to: St. Thomas More School 11822 Holmes, Kansas City, MO 64131 Attn: Luke Bresette Fund