The most important thing to rule out (preferably within the first 24 hours) is NOT a nasal fracture, but a septal hematoma. If there is a collection of blood under the lining of the septum, that can interrupt the blood supply to the cartilage, resulting in loss of cartilage and long term collapse that can be very difficult to repair. It's easy to diagnose this by looking in the nose, and it can be drained easily. It is also very uncommon, I almost never see this in children with a broken nose.
Assuming that the only injury is a fracture of the nasal bones, not a more involved fracture of the other bones of the face, I don't make any decisions regarding treatment for 2-3 days. I don't usually even see the patient before then, because you really need to wait for the swelling to go down. Ice packs for the first 24 hours, then warm packs.
An x-ray is almost always useless. The diagnosis is made by the physical exam and history. Often times an x-ray will miss a fracture, or an old healed fracture will erroneously be read as a new fracture.
Once the swelling goes down, if there is an acute change in the appearance of the nose - that is, the nose is shifted off to one side as compared to before the injury, then that means that there is a displaced nasal fracture. This is treated by a closed reduction, in which the nose is pushed back into position and splinted with a cast or other splint. In children, this is done under general anesthesia, in adults it can sometimes be done with local anesthesia. I leave the splint on for one week and tell the patients to avoid contact sports for a total of two weeks from the surgery. You have a very limited window of opportunity for this reduction - once the bones heal in place (7-10 days after the fracture), you can't just push them back into position. After than you would need a formal rhinoplasty, which would involve refracturing and resetting the bones.
If the nose seems broken (i.e. painful to touch 3 days later, with staining of the skin under the eyes), but is not displaced, then I just recommend avoiding contact sports for 2 weeks while the bones heal.
Good luck! Feel free to PM me if you need a local referral...
Mike