What could cause my toddler to have a sore mouth. strep throat swap was clear?

Most are viruses: Toddlers are constantly chewing/sucking their fingers or touching the world around them.That gives them ample opportunity to sample every virus or bacteria that exists in their environment. Their mouth/throat is the entrance to their immune system and tonsils that react when stimulated. Strep is sensitive to antibiotics but the viruses must run their course.

Other causes: If it is a sore throat and was negative for strep it is likely a virus but could also be other causes of sore throat that presumably your doctor would have looked for. Symptomatic treatment with analgesia and cold drinks, ice blocks may help.

Sore throat : Most common cause in toddlers is a viral infection. Pain relief and fluids should help .