Every kid dreams about being a hero. It is okay for them to look up to comics superheroes like superman or spider-man. But they should also know the value of regular every day heroes in the community like policemen or firefighters.
Aside from buying them comic books and caped costumes, it is also a good idea to buy them the things that regular heroes also use. You could also introduce them to the valiant people who risk their lives in the line of service by bringing them to places like fire stations. Choosing toys like firetruck pedal cars are also a good idea.