Suppose that a little kid found him/herself in a traumatic situation at an age of which he or she has no conscious memories (let's say between 1 and 3 years old). For example, the kid was put in a situation where the little one experienced a lot of fear (of course you can ask if a very young kid can experience fear, but I can assure you it can). Maybe its mother wasn's paying attention to him/her while it was playing on the beach and a "mad dog" (who maybe was treated badly by his/her boss while being a puppy) attacked the poor one, while at the same time a police car with its siren on maximum volume was driving along the boulevard near the beach. Our kid grows older and when old enough he/she notices that every time it hears the loud sound of a police car's siren a feeling of "unusual" (I mean, everybody gets a little frightened when hearing the siren's sound, though less in the city than someone who never heard the sound before high fear comes bubbling up (I found myself in a very stressful situation when I was a kid of which I can remember nothing; I know this because my mother told me). The question is somewhat similar to this one but certainly not a duplicate.
Now, is there a way to determine if the story I told can be true and, if so, can we find out what the traumatic event was (assuming that no one told you, as my mother did; this is, by the way, the reason I know almost certainly that the story can be true)?