What difference do you notice between the reaction of the adults and the children when faced with danger?
Let's assume for a minute that both the children and the adults are aware of the fact they are in danger. I think the most obvious difference is the admittance of fear, coming from the kids. Adults internalize fear and often become very quiet in dangerous situations. Seldom do they immediately ask for help. Instead, they try to solve the problem alone. Young children, I think, are more apt to admit they are afraid and to seek help immediately, especially if they have grown up in an environment where immediate help (and protection) has been available.
In addition to what the other posters have said, children sometimes recognize danger, but fail to recognize their own mortality. This means they thrive on making choices that seem dangerous and exciting, but they have no real concept that their actions could lead to their own death or the death of others. Many adults have learned this lesson, and they are sometimes better at making choices based on consequences. This does not hold true for all adults and children, but it does hold true for many of them.
Sometimes children do not know that they are in danger, and sometimes they are afraid of things that are not dangerous. It comes down to cognition, what they can understand, and experience, what they have lived. Some adults have irrational fears, and sometimes these are based on childhood trauma.
In general, children do not seem to understand what is dangerous as well as adults do. Children will be very afraid of things that really cannot hurt them. At the same time, kids can be fearless. They often do not understand when they are doing something that is very dangerous.
Also, when kids think something is dangerous, they tend to be very afraid of it, to the point of being unable to function. They react much more fearfully to danger than adults do.
Post 4 hit the nail on the head...remember when you were 17, knew everything, and couldn't be killed? Kids, and teenagers ESPECIALLY don't see danger, they see either confrontation, or a challenge.