The Billboard Music Awards worked a delicate balance Sunday night between serious issues like school shootings and suicide and the usual “Let me hear you make some noise!” awards-show fare. In the show’s second moment addressing the recent epidemic of school shootings — following Kelly Clarkson’s tearful introduction — Shawn Mendes and Khalid were joined onstage by the show choir from the Marjory Stoneman Douglas High School in Parkland, Fla., where 17 people were killed by 19-year-old Nikolas Cruz in February. Mendes, 19, and Khalid , 20, performed “Youth,” their duet from Mendes’ forthcoming self-titled album, out Friday. It includes positive yet defiant lyrics like “You can’t take my youth away/ This soul of mine will never break/ As long as I wake up today/ You can’t take my youth away … I won’t let it turn into hate, I won’t let it change me.” While the song doesn’t directly address gun violence, there was no question about the meaning: Khalid wore a t-shirt that said “Protect our children,” with the word “guns” placed above “children” and crossed out. The choir wore black shirts that simply said “Youth.” During the performance several people in the crowd were seen tearing up, including Halsey. The song ended with Mendes and Khalid embracing the members of the choir.