Clint Barton becomes the superhero Hawkeye when he puts on his costume. And the costume that Jeremy Reener has in the Avengers 2012 movie (Avengers Assemble) is very cool!
He wears a black leather or PVC outfit and cool dark shades.
Hawkeye is the ultimate archer so he also has a bow and quiver full of arrows.
There's an official Avengers Hawkeye costume for grown ups but we haven't found one for kids so we'll have to improvise. There is an official Hawkeye toy bow though, we'll take a look at that too.