The Avengers star, who plays villain Loki in the Marvel Comics films, flew in from London to attend the advanced screening and pay tribute to organisers at the Variety the Children's Charity of New York and The Children's Aid Society.
Speaking after the event, he said, "I just landed from London... and to sort of come through the airport, throw on some clothes and come into that response (at the cinema) where there were just 300 kids so excited to be there. To see that enthusiasm, to see them clap and cheer, wearing Loki T-shirts and swinging hammers, that was really gratifying.
"For charities like Variety of New York and Children's Aid Society and Unicef, who I have done some work for, I believe so strongly in their work. There are armies of people behind the scenes who do tireless work on behalf of children all over the world. So it's nothing for me to turn up and introduce a screening for them. I hope it's a nice reward."
Thor: The Dark World, which also stars Chris Hemsworth and Natalie Portman, hits U.S. theatres on 8 November (13).