I assume it is more of the "if the parent leaves me, I am going to die" reflex that is ingrained in babies, so the danger is great enough to warrant panic, even though it is improbable. Plus, very young kids don't have object permanence.
I heard of a parent telling a young kid that beyond the turn on the road there is a Foobarator, and kid dutifully keeps within safe distance without knowing what's a Foobarator nor what threat it poses.
I remember at age 7 being afraid of tigers and dinosaurs at night, sometimes I watched tall coconut trees. I also asked my mum if she will abandon me for a mistake.
