Answer: Parents or Guardians
Step-by-step explanation:
This is most likely addressed to the parents of the students in this school as it is the parents or at least the legal guardians, that usually bear the responsibility of dropping students off at school and picking them up.
The notice is asking parents to ensure that they drop off and pick up their children early enough. The most effective place to deliver such a message would be a Parents Teacher Association (PTA) meeting.