There is a sour smell in the baby’s mouth, consider halitosis to be investigated. The causes of bad breath, consider the following: 1. If improper feeding causes gastrointestinal dysfunction in children, it can lead to bad breath. 2. Inflammation of the gastrointestinal tract. If infants and children eat an unclean diet, there is a bacterial infection that causes inflammation of the gastrointestinal tract, which can also cause bad breath. 3, abuse of antibiotics. If a child uses antibiotics because of a bacterial infection, it can lead to dysbiosis of the gastrointestinal flora, which can easily cause bad breath in children. 4, weather changes. The weather becomes cold and the child’s abdomen gets cold, which can cause indigestion and can also lead to bad breath.