old think: Clean the wound thoroughly using hydrogen peroxide, then leave the cut uncovered and just let it heal in the open air.
new think: Wash the wound with soap and water.
why: Foaming peroxide won't wash the dirt out; in fact, it kills white blood cells along with bacteria, which may increase the risk of infection. Once they´re clean, superficial abrasions like skinned knees can be left open, but cover anything deeper with an antibiotic ointment (such as Neosporin or Bacitracin) and a bandage. Remove the bandage at night (because kids will be less likely to pick at the cut in their sleep) to allow the wound to dry.