Every night the maintenance man would remove them and the next day the
girls would put them back.

Finally the principal decided that something had to be done. She called
all the girls to the bathroom and met them there with the maintenance
man. She explained that all these lip prints were causing a major
problem for the custodian who had to clean the mirrors every night (you
can just imagine the yawns from the little princesses). To demonstrate
how difficult it had been to clean the mirrors, she asked the
maintenance man to show the girls how much effort was required.

He took out a long-handled squeegee, dipped it in the toilet, and
cleaned the mirror with it. Since then, there have been no lip prints
on the mirror.