3 year old little boy passed away unexpectedly

Me

This little boy parents took him to the doctor at the emergency room because he wouldn't eat,or drink, since he was vomiting but the little boy parents sent him to school the next day where he couldn't hold his head up due to dehydration but anyway he passed away yesterday morning in his sleep. his baby sister found him! sad situations...im just wondering if the boy had heart problems and didn't know it or if he had this flu mess.