The superintendent of Burlington schools said the district is investigating whether an employee failed to promptly report information about a relationship between a high school student and a former Spanish teacher. Giovanna Yaranga pleaded guilty Friday to four misdemeanor counts of sexual exploitation of a minor. She was fired in June. The superintendent said an investigation found that an employee had information that the district believes should have been reported. Staff who have ‘‘reasonable cause to believe’’ that child abuse is occurring, including a sexual relationship between a teacher and a student, must report it to the Department of Children and Families within 24 hours.