Which endocrine gland is responsible for the release of a hormone that stimulates t-cell development and proper immune response in children?
a. testes
b. adrenal glands
c. pancreas
d. thymus

The correct answer would be d. thymus.

The thymus is a specialized lymphoid organ of an immune system.

It serves as the site for training and maturation of T-lymphocytes or T cells.  

It is composed two identical lobes each containing outer region termed as cortex and inner region termed as medulla.

T-cells are first trained and selected in the cortex region via positive selection. In this, T cells which are able to bind to foreign antigens are selected and rest are degraded.

The selected T cells then move in the medulla region where they are selected by negative selection. In this, the T cells which binds to self-antigens are degraded and rest survive to become functional T cells.