What are the causes of a toddler to get swollen gums and lips and white sores in their mouth?

Virus: Sounds like initial exposure to the common herpes simplex virus which almost universally present in our population. Have your pediatrician check your child.

A viral infection: Viral infections could be aggressive and target the mouth and throat, making it uncomfortable for toddlers to even eat.

Virus: This could be primary herpetic gingivostomatitis the initial presentation of herpes simplex virus. The beginning of 'cold sores'.

Hand foot and mouth: A common cause of this is called hand foot and mouth disease. Cocksackie virus is the most common cause. Fever, mouth sores and blisters on hands and feet are seen. Push fluids and motrin for pain are the mainstays of treatment. This is self limited! Baby should be better within a few days.

Dr Upadya and another doctor agreed