Final answer:
The thymus gland is largely operational in childhood, playing a key role in the development of the immune system by producing thymosins that aid in the maturation of T-cells.
Step-by-step explanation:
The gland that is largely operational in childhood is the thymus gland. The thymus plays a crucial role in the immune system by being involved in the development and maturation of T-cells. During infancy and early childhood, the thymus is larger and more active. It produces a group of hormones known as thymosins, which contribute to the development and differentiation of T lymphocytes, vital cells for the immune response. While thymosins are found in other tissues and have various functions, their production in the thymus helps establish the immune system during the critical growth years of childhood. It is an organ of the immune system that is involved in the development and maturation of T-cells, which are immune cells. The thymus gland is particularly active during infancy and early childhood, and then begins to atrophy as we age.