Does he complain of any pain in right side of stomach or stomach itself is getting hard? Some
liver and gallbladder diseases present with greenish (bilious) vomiting. But since it's just one episode, no need to be overtly concerned about. Just treat him with paracetamol syrup and if such greenish vomiting continue, get an
LFT and Ultrasound of abdomen and review with your pediatrician.