What are the symptoms of a child with a underactive thyroid gland?

Lab test essential. A child with hypoactive thyroid may have constipation, delayed growth, poor cognitive skills, large tongue etc. However, clinical signs and symptoms are not a good indicator of thyroid function. If there is any doubt, easily available and not too expensive tests, e.g., TSH and free T4 are essential for a proper work-up.
Hypothyroidism. Similar to adults with 2 major exceptions: often hypothyroidism leads to failure to thrive or lack of weight gain vs adults which usually causes weight gain. Secondly, poor growth is often seen. Other symptoms like fatigue, dry skin, coarse hair, hair loss, forgetfulness, moodiness, constipation, cold intolerance, and exercise intolerance are similar to adults.