Hi. Thanks for your query. Your history is classical that the boy who is just 4 1/2 years had a bug bite and developed edema on the very top par of the scrotum on the same side. The leg is very swollen and red. The edema or the inflammation might have traveled from the leg through the lymphatic channels to the said part. If only the top part of the scrotal skin is involved, there is nothing much to worry about. Consult a Pediatric surgeon and get an ultrasonography of the area of scrotum and the lower limb too. Get started with appropriate treatment and let us have the regular follow up and see what happens next.