The Land Before Time/Nightmare Fuel


 * The tar pits. Seeing all the innocent, rather young protagonists getting submerged in black gunk and nearly losing their lives is not a fun thing to watch at the age of 6 or in your adulthood. The 'tar monster' that the characters form to frighten' Cera is also pretty morbid in appearance, and definitely isn't pretty to look at, either. It looks like some sort of Eldritch Abomination, honestly. Made worsedue to the horrifying noise made by the "tar monster".
 * Another equally scary thing was the T.Rex. It freaking chased the heroes through half of the movie.