So why did chico have the headphones plugged in his chest?
Because the Sandinistas had a hard time finding enough food in the jungle, Chico suffered from malnourishment, which made him shorter than kids of his age. Chico and Amanda called their father "mi viejo" Spanish: "my old man". Amanda didn't intend to take him with, but he didn't have anyone else to look after him, and he also wanted to join his father's revolution.
Chicos absence has really peaked my interest, but it appears the rest of internet is less interested, because I could'n't find anything of note. I can't find anything cohesive about his 'Chest Jack', presumably something to do with parasites. His apparent death seems a bit too easy, and he is practically written out of The Phantom Pain. Does anyone have any good theories worth sharing?