It is not uncommon for children to have fractures, and these may range from a simple buckling of the bone to the bone actually coming through the skin.
It is important to stabilize the injury in the position found. If there is an open bleeding wound, apply a clean compression dressing to control bleeding. Do not attempt to wash the site or push the bone back in place.
Immediate medical attention should be sought for fractures in which the bone comes through the skin, there is obvious deformity, or there is numbness or blue discoloration distal to the fracture. If there is associated back or neck injury, do not move the patient, call 911.
For less severe injuries, ice and elevate the injured arm and call your physician for further instructions.