In 2009, U.S. hospital emergency rooms treated an estimated 8,800 people for fireworks related injuries; 53% of 2009 emergency room fireworks-related injuries were to the extremities and 42% were to the head. Children ages 10-14 have the highest risk for injuries, with more than twice the risk for the general population.
The National Fire Protection Association has teamed up with the American Academy of Pediatrics and other health and safety organizations under the umbrella of the Alliance to Stop Consumer Fireworks to persuade people to "leave fireworks to the professionals."
Here is one of many videos the NFPA has released to illustrate the hazards to amateurs of setting off fireworks: