The correct option is A Loss of cell-mediated immunity
Damage to thymus in a child would lead to loss of cell-mediated immunity. Thymus gland is responsible for the differentiation and maturation of T-cells. These T-cells helps in fighting infections in the body. If any damage occur to the thymus gland, then child would be more prone to infections due to decrease in the number of T-cells.
So, the correct answer is 'Loss of cell mediated immunity'.