I would not use lice treatment on my children "just in case". What I would do is slather them with some goopy hair grease or gel while it works it's way through the class. Lice don't tend to like goopy hair. I vaguely remember reading that they hate tea tree oil too. Good luck avoiding them.
"Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind." -- Theodor Seuss Geisel