The thymus is located in the upper part of the chest. It is made of two lobes that join in front of the trachea. The thymus is an important part of children's immune systems. It grows larger until puberty and then begins to shrink. The gland produces thymosins, which are hormones that stimulate the development of antibodies. The thymus produces T-lymphocytes which are white blood cells that fight infections and destroy abnormal cells.