This is difficult cause the truly terrifying 1 was Terminator 2 (the bomb drop) but I found these to be up there as well: Poltergeist, Watership down, and Killer Klowns from Outerspace. The difference is as a child I understood reality pretty well, and knew a bomb drop was realistic vs some ghost.
In honor of scary media month: what is the first piece of media you remember truly frightening you as a child?