Despite its frequent association to middle-aged or older groups of individual, there is still a possibility of younger group to develop underactive thyroid gland. These groups of individuals may include teens and even infants. To some extent, neonates with decreased thyroid production may present with jaundice, frequent choking, protruding tongue, constipation, poor muscle tone and excessive sleepiness.

Such symptoms must be immediately suspected as pointing to hypothyroidism in newborn babies. Lateness in diagnosis and treatment may result in considerable consequence on the future growth of the baby. Several physical and mental retardation have been associated with untreated hypothyroidism. Unawareness of the symptoms of hypothyroidism may leave lifetime regret on the part of the parents. When the onset of hypothyroidism occurs during childhood, there are some common signs and symptoms to anticipate. They include poor growth. Children with untreated hypothyroidism tend to have shorter stature and delayed development of permanent teeth.

In general, teens with hypothyroidism may present additional burdens for the parents and family. General symptoms of hypothyroidism in teens include delayed puberty and poor mental development. Even when they have relatively normal mental development, persistent weight gain may result in depression and low self-esteem. Physical effects like dry skin, hair loss, and muscular weakness and social isolation and inability to join their peers may induce more serious mental effect. Teens with hypothyroidism have been reported to have poorer performance at school compared to their peers.