the facts you are giving are pretty sketchy. it sounds as though your son was giving other kids at his school medicine that was supposed to be used by him. you wouldn't have a case against anyone based on those facts. i hope this helps and that all of the kids, including your son are ok.
If I understand your question is that your son was given medicine at school that was not his. Unless your son suffered damages, there really isn't any point of a lawsuit as there are no damages. Although it was wrong, it appears no one was harmed. If your son suffered damages, then you possibly have a lawsuit and should consult with an attorney that handles personal injury cases.
Answers to AVVO questions are for general purposes only and do not establish an attorney-client relationship. This answer is not a substitute for legal advice and should not be relied upon without a full consultation with an attorney that can fully look at issues involved.