2 Corinthians 11:13-15 ~ "For such men are false apostles, deceitful workmen, disguising themselves as apostles of Christ. 14 And no wonder, for even Satan disguises himself as an angel of light. 15 So it is no surprise if his servants, also, disguise themselves as servants of righteousness. Their end will correspond to their deeds."
Roughly 1 minute considering verses of the Bible, and I, a dad, would explain them to my sons.