FThyroid hormone Promote expression of the gene for growth hormone in somatotrophs. T3 is required for the production of both growth hormone and insulin-like growth factors. It is also required for the action of insulin-like growth factors on epiphyseal cartilage. They stimulate the linear growth of bones and endochondral ossification and maturation of epiphyseal bone centers.
Therefore, hypothyroidism lead to dwarfism in children, and the mental status of the child will be also altered (low).
In the case of hyperthyroidism initially, there will be the growth of the child due to the synergetic effect of growth hormone but thyroid hormone will close the epiphyseal plate of the bone early than a normal thyroid hormone child. Therefore the child will be dwarfed in his/her life but the mental status will be active in this case.