Sports injuries are among the most common causes of a broken collarbone. Other frequent causes are falls and car, motorcycle or bike accidents. The time for a broken collarbone to fully heal depends on the severity of the injury. In children, complete healing may take as little as three to six weeks.In adults, six to 16 weeks or more are often necessary for a collarbone to heal solidly.Unfortunately, during that time there is no way to completely immobilize a collarbone fracture to keep it from moving and, thus, speed healing, as can be done using a cast on other broken bones, such as a wrist, arm or leg.n children, complete healing may take as little as three to six weeks. In adults, six to 16 weeks or more are often necessary for a collarbone to heal solidly.