In the chaos of Tony snapping the gauntlet, rushing him to the nearest hospital and the reality of having saved the universe, the Avengers forgot to actually tell Peter that Tony had survived. Now he's missing and nobody can find him to tell him that Tony survived.
Peter Parker gets forgotten on a Field Trip, his class leaving him behind at the Avengers Tower. But it's okay, because his hero Tony Stark will get him home.
Tony Stark had made it possible. Spent endless hours, sleepless nights and caffeine induced days to bring the Rogues home and here they were. However there is one thing he forgot to do. Tell Peter.