I always told them "I'm just here for the awkward moments". We had a great time in my class and I like to think the kids learned a lot. Who knows if they remember it or not but they always did well on the state tests.
You just can't take things too seriously and you can never be surprised at what might come up in class. I taught science. My all time favorite line came out when I was teaching about metabolism -ingestion, digestion, respiration, and excretion.
A kid raised his hand and in all seriousness asked, "What the crap is excretion?"
Now if the situation described in the parent post had come to my attention, you bet there would have been swift action. First place to start is always with the parents. About 90% of the time they come up with great solutions.