Should I Be Concerned About A Child Swallowing A Coin 4 Days Ago, Has Normal Bowel Movements But Now Has Green Stool?

Hi goodday my 4 year old swallowed a coin 4 days ago and now his stool is green ...He s been passing stool normal since he s swallowed the coin..Can you tell me why his stool is green?? Should i be worried ...Can the coin get inside his appendix?? Please help...