With Spider-Man: Homecoming only having recently come out, there have been a lot of opportunities for Tom Holland to do these sorts of things, just like Captain America and Iron Man before him.
Marvel does a lot of these sorts of things in order to acknowledge the many kids who are fans of the many movies in the MCU.
With Thor: Ragnarok and Black Panther coming up, presumably there will only be more moments like these coming down the pipeline, as well..
Just about a month ago, we saw Tom Holland visit sick kids at the Children’s Hospital in Los Angeles; at another point, the actor who plays Spider-Man acknowledged fans in the only way he could: by throwing autographs out of his hotel window.