Mycotic aneurysms, also called infected aneurysms, are localized irreversible vascular dilations caused by arterial wall infection with subsequent vessel wall weakening. They are rare but potentially life-threatening conditions that can occur from bacterial seeding into an intact vascular wall or superinfection of a pre-existing aneurysm or atherosclerotic plaques. Risk factors in children include coarctation of the aorta, in-dwelling arterial catheters, postcardiac surgery, or immunosuppressive states. We report a rare case of an abdominal aortic mycotic aneurysm in a four-year-old patient with concurrent pericarditis. Her nonspecific presentation with fever and body pains posed a diagnostic and therapeutic challenge. We discuss the risk factors, diagnosis, and management of this condition.