The terms "children" and "child" don't imply high schoolers, let alone seniors. In high school, I think it's okay for teacher's to express their opinions as long as they are clearly identified as opinion and not fact. When this happens, all students should feel free to express their opinions and perhaps have some healthy, civil debate on topics of interest.
My 12th Grade IB History teacher would show us films that are clearly biased to the left of American political spectrum. We had to watch Outfoxed, Sicko by Michael Moore, and Al Gore's An Inconvenient Truth and write essay responses to them. That's inappropriate if the information is one-sided like that. I don't care how old a student is; teachers shouldn't be teaching political opinion as fact.