Any particular scare, of course, might combine two or all three of these types. The first type, instinctive fears, arise from the unexpected. When startled, instinctive fear causes a physical reaction. The fears of children, especially of infants, are predominantly instinctive. They are physiological reactions to external stimuli, and they have nothing to do with conscious thought.
Instinctive fears are basically beyond our control.
A purely physiological reaction raises our heart and respiration rates, our blood fills up with adrenalin, and so on. He who knows no fear gets eaten by lions. They also begin to understand that some things are beyond their control, and they develop a more conscious sense of fear. Some of these fears are quite rational. By definition, a rational fear is derived via logic, from factual evidence.