Because so many older doctors have retired or are retiring because of the difficulty in practicing, childhood diseases are not something that most younger doctors have seen. Immunizations have been wonderful in protecting children unless the parents refuse them.(We owe Dr. Salk and Dr. Sabin and the others who have developed vaccines a great thanks for their work.)
When I was a resident in pediatrics, I was married and had two children. Both children had had measles and mumps, because vaccines were not available. I was on ward rounds with an attending staff doctor who specialized in developmental problems. One little boy looked quite ill and to my eye had had regular measles or rubeola. The attending doctor said he though it was an allergic dermatitis. The child had a fever and all the signs of rubeola. I spoke up and said I thought he had regular measles. The child was on an open ward, so it was important that he be moved and treated for the disease. The attending doctor was upset with me but agreed to call the infectious disease doctor. That doctor agreed with my diagnosis and I was never the attending doctor's favorite after that.
When I had my own pediatric practice, a mother brought her child in and said she had been diagnosed as having mumps. The location of the swelling didn't seem right to me and I suspected the child had an abscess in one of her teeth. The mother immediately contacted the child's dentist and the abscess was treated. The "mumps" was cured.
Another time when I was consulting in a Navy muscle disease clinic, I was presented with a child the resident doctor diagnosed as having muscular dystrophy. The muscle weakness was not symmetrical, as occurs in muscular dystrophy. I asked the parents if cases of polio had occurred when the child became weak. They said "Yes" and the boy had also had a fever. The diagnosis was polio, not muscular dystrophy. So a second opinion is often a very wise thing to get, particularly from an older physician.