Cold, diarrhoea, and dehydration together in a child are commonly caused by viral infections or stomach infections, and the most important part of treatment is preventing dehydration and keeping the child comfortable. Give plenty of fluids in small amounts frequently, such as ORS (oral rehydration solution), breast milk, formula milk, clean water, rice water, or soups, depending on the child's age. ORS is especially important because it helps replace the water and salts lost through diarrhoea. Continue regular feeding because children recover faster when they keep eating light and nutritious foods like rice, banana, curd, khichdi, applesauce, or toast. Avoid oily, spicy, junk food, and sugary drinks because they can worsen diarrhoea. For cold symptoms, keeping the child rested, using saline nose drops, steam in the room, and giving warm fluids may help relieve congestion. Do not give antibiotics, cough syrups, or anti-diarrhoea medicines without medical advice because many childhood infections are viral, and some medicines may not be safe for children. It is important to seek medical help immediately if the child has difficulty breathing, a very high fever, repeated vomiting, blood in stool, severe sleepiness, dry mouth, sunken eyes, very little urine, an inability to drink fluids, seizures, or worsening weakness, because dehydration in children can become serious quickly. With proper hydration, rest, and supportive care, most mild infections improve within a few days.