The study showed children often believed their own powers had been given a "super-boost" by wearing the costume, provoking extreme risk-taking behaviour.
The research, by a group of British doctors working in accident and emergency, looked at five cases of boys who had injured themselves while dressed as Spider-Man or Superman.
One six-year-old suffered a head injury and a broken foot when he fell from a first floor window-ledge pretending to be Spider-Man. Three other boys, aged three to eight, sustained broken bones while trying to fly "without having planned for landing strategies".
Anatomically correct costumes, with foam muscles, had spared two of the children from further trauma because of extra padding.
The authors suggest that the parents of Spider-Man fans keep their windows locked. They also warn that a child with a Bob the Builder outfit might want to play with hammers and saws.
The report, published this week in the Archives of Disease in Childhood, noted doctors had not treated any girls imitating superheroes, as commercial role-models were not generally risk-taking. There were no My Little Pony-related injuries.
The case report was compiled by Dr Patrick Davies, from the department of paediatrics at the Queen's medical centre in Nottingham, and doctors at Derby children's hospital and Royal Bristol children's hospital.
The study concludes: "Parents, should be aware that a superhero costume can provoke perceived super-abilities which need special supervision."
Roger Vincent, a spokesman for the Royal Society for the Prevention of Accidents, said children wanted to copy their fantasy heroes, whether or not they donsned the appropriate costume.He said parents and carers should chat to children about the difference between fantasy and reality.
* Archives of Disease in Childhood http:adc.bmj.comcgicontentfull923242