A Fatal Feast

Two skeletal boys wandered out of the war-torn ruins and met a squad of friendly soldiers. Pitying the starving children, the young recruits eagerly handed over all their canned meat, biscuits, and chocolate. The older brother smiled warmly as he watched the younger one eagerly devour the feast. A few hours later, the younger brother died in sheer agony. The military rations were perfectly safe, untouched by poison or rot. Who killed him?