When a child has watery diarrhea, start giving fluids right away. Liquids and watery foods like thin cereal porridge or gruel, teas, soups, and even plain water can help. If your baby is dehydrated, keep giving breast milk often. Don't give plain water to a baby under 6 months of age. Giving water instead of breast milk could lead to diarrhea. It also won't provide the nutrients the baby needs to grow.