Treatment for this case is based on the clinical picture.
There is an increased fat pad anteriorly and a posterior fat pad (which is pathological). The question is whether this is secondary to a supracondylar fracture or to a radial head fracture (or neither).
There is a question if the angle of the distal humerus is heightened (consistent with a supracondylar fracture), but then this would be a minimally displaced fracture.
If the pain is in the proximal forearm and there is good range of motion, then this is likely a radial head fracture (or even just a contusion) and a sling is sufficient.
If, on the other hand, the pain is more over the elbow and distal upper arm and there is marked swelling, the best approach is a posterior cast splint from the upper arm around the elbow to the forearm.
Given the pain and limitation of range of motion, a posterior slab was applied in the urgent care clinic and the patient was referred to orthopedic follow-up for reassessment of the situation the next day.