Why are children more resistant to mortality from severe infections?

[...]in the context of evolution, prepuberty is a unique life-stage characterized by specific energetic goals. The potential for estrogen to have sex-independent effects on the immune system is logical, considering the essential role that it plays in the pubertal development of both sexes. Challenging environmental conditions like famine or infectious disease can halt or in some cases expedite sexual development (16). [...]the discussion of evolutionary perspectives above emphasized the potential influence of changing metabolic and energy requirements on the immune system.