Hand, Foot, and Mouth Disease (HFMD): Caused by Coxsackievirus A, this condition is characterized by oral sores, sore throat, and can be accompanied by diarrhea, especially in children. The combination of symptoms and the commonality of HFMD in pediatric populations make it a leading consideration.

Herpes Simplex Virus (HSV): HSV can cause oral sores (cold sores or fever blisters) and, less commonly, sore throat. While diarrhea is not a primary symptom, it can occur, especially in the context of primary HSV infection.
Enterovirus: Besides HFMD, other enteroviruses can cause a range of symptoms including sore throat, oral sores, and gastrointestinal symptoms like diarrhea.
Adenovirus: Known for causing a variety of illnesses, adenovirus can lead to symptoms such as sore throat, oral sores (herpangina), and diarrhea, particularly in children.

Herpangina: Although already mentioned under adenovirus, herpangina caused by Coxsackieviruses is crucial to consider due to its potential to cause severe symptoms, including high fever and significant discomfort.
Infectious Mononucleosis (Mono): Caused by Epstein-Barr Virus (EBV), mono can present with sore throat, fever, and sometimes gastrointestinal symptoms. Oral sores or thrush can also be present, especially if the patient's immune system is compromised.

Cytomegalovirus (CMV): While CMV can cause a wide range of symptoms, including sore throat and diarrhea, it is less commonly associated with oral sores compared to other viruses. However, in immunocompromised patients, CMV can cause more severe and varied symptoms.
Human Immunodeficiency Virus (HIV): Acute HIV infection can present with non-specific symptoms including sore throat, oral ulcers, and gastrointestinal symptoms like diarrhea. Although rare as a primary diagnosis for these specific symptoms, considering HIV is crucial due to its long-term implications.