Would a regular pediatrician be able to detect something serious like cancer and be able to inform a patient about it?

Hi Anisa, although my education is in engineering and computer science, I'm going to take a shot at answering your question.

Cancer often has pronounced and dramatic symptoms, which most doctors are trained to recognize. When they do, they will order additional diagnostic tests, such as a blood draw and analysis, a surgical extraction and biopsy, or a PET scan, to determine more clearly what's going on within the body and immune system. If the initial diagnostic tests indicate potential cancer, the doctor will usually inform the patient that there is cause for concern and refer the patient to an oncologist (a cancer doctor) for further examination and to determine treatment options. Of course, giving and receiving a cancer diagnosis is never easy, but I suspect doctors receive training on how to inform patients in the best manner possible. That's my general understanding on the topic, I hope it helps answer your question.