If a baby has a fever with blisters in the mouth, it may be caused by viral infections. The more common causes are herpes virus infections, which tend to occur in children with low immunity and resistance, and can sometimes be transmitted through contact and respiratory droplet transmission. Therefore, during the infectious season, it is important to drink plenty of water, wash your hands more often, and do not go to crowded places to avoid cross-infection. When the mouth blisters, there will be pain and crying. It can be treated with anti-viral ointment and oral medication, such as ribavirin and anti-viral oral medication Pu Dilan Anti-inflammatory Oral Liquid.