Maybe those kids could use a Bible verse or two:
Matthew 7:15
"Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves."
Matthew 24:11
"And many false prophets shall rise, and shall deceive many."
And maybe the most appropriate:
Matthew 24:24
"For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect."
Jeremiah 14:14
"Then the Lord said unto me, The prophets prophesy lies in my name: I sent them not, neither have I commanded them, neither spake unto them: they prophesy unto you a false vision and divination, and a thing of nought, and the deceit of their heart."