If a four-year-old baby has diarrhea, the measures to deal with it are as follows: First of all, if the baby’s appetite is okay, you should try to let the baby drink more water as well as eat normally. When diarrhea occurs, a large amount of water is excreted with the stool, which can easily cause dehydration, so let your baby drink more warm water if possible. In addition, if you have probiotics at home, you can give your baby oral probiotics to regulate the intestinal flora. If the stool is thin and watery, you can give your baby oral montelukast. If your baby’s stool contains mucus or even pus and blood, you should take the stool to the hospital for laboratory tests as soon as possible to see if there are any white blood cells in the stool, etc. If your baby is in poor spirits, has dry lips and mouth, and has significantly reduced urine output, it means that dehydration has occurred and you need to seek medical attention immediately. The above questions are for reference only. Please refer to the doctor’s instructions for specific medication and treatment.