There are more reasons for 3-year-old babies to be blue around the nose, and the common ones can be low temperature, trauma, congenital heart disease and so on. 1. Low temperature: If the weather is cold, it can cause the blood circulation in the nose is not smooth, the local capillary contraction. This can lead to the phenomenon of blue around the child’s nose, and does not require special treatment. 2. Trauma: Trauma to the baby due to walking and falling, playing and trauma, bruising can occur, resulting in bruising around the nose. 3. Congenital heart disease: with congenital heart disease, babies may show symptoms of a blue nose and bruising around the mouth. 4. Other: some babies may be overworked, etc., and may also show symptoms of blue around the nose. This situation does not ease, you need to go to the hospital in time, under the guidance of the doctor for treatment. Attention to rest in daily life, diet needs to be nutritionally balanced.