Some common causes of blue lips in toddlers are exposure to cold, lack of oxygen, anemia, asthma and bronchitis, states Right Diagnosis. Other common causes include pneumonia, heart conditions, coughing, shock and croup. A child's lips are supposed to be pink in color; hence, blue lips indicate that something is wrong, and the condition requires immediate medical attention.
Another common cause of blue lips in toddlers is cyanosis. Cyanosis is an indication that a toddler doesn't have enough oxygen in his blood, notes SheKnows, and may signal a problem with the lungs, heart and airways. Medical tests such as pulse oximetry, chest X-rays and EKGs can measure the oxygen level of toddlers and help doctors locate any internal problems with the toddler's heart.
Blue lips in toddlers can also be caused by being at a high altitude, seizure, or a blood problem such as abnormal hemoglobin and polycythemia, according to the U.K.'s National Health Service. Polycythemia is characterized by a high concentration of red blood cells, while "abnormal hemoglobin" is a term that means that the blood cannot take up enough oxygen. Not all instances of blue lips in a toddler are fatally serious, but it indicates that something is out of the ordinary with the toddler.