Parents need to know that this is a downbeat horror feature, with a child complicit in his (adoptive) mother's own death and evil triumphant in the end (with the qualifier that it was conceived as just the first in a series of films, so it's just the opening installment, not the whole story). It casts a small boy in an especially negative light as the literal antichrist, for whom the only fair treatment, according to this, is a ritual execution by knife. The gory deaths and injuries, including decapitation and impalements, were considered shockingly explicit in their day.

Families can talk about why this movie was popular. Do you think it's a "religious" film in any sense? How does it compare with the Left Behind book-and-movie-and-radio blockbuster series? You can look up the Bible passages and interpretations this movie cites to see how Hollywood played fast-and-loose with Scripture, and maybe study what historians have to say about Satanic lore and its popularization by both church authorities and horror-storytellers.