My earliest Halloween memories involve a Superman costume and a Batman costume my brother and I, respectively, wore one year. I kept the costume for years after that, wearing it around the house as long as it would fit, then eventually passing it down to my youngest brother. I had one of those cheap plastic Batman masks that obscured my vision and was probably some sort of fire hazard, while my brother got to go maskless ... because unlike the kid in the above picture, we knew Superman didn't wear a mask.
Ah, memories ... if you have similar ones, you may enjoy checking out Growing Up Heroes, a blog that features kids dressed as various superheroes between 1960 and 1990. Everyone from Batman, Spider-Man and the Hulk to various Star Wars and Star Trek characters are represented, as are various costumes, shirts and, of course, Underoos.