In general, how would a 10-year-old child be a more reliable eyewitness regarding the facts of an event than a 40-year-old adult, and vice versa? why?

I believe that a ten-year-old would be a better eyewitness because generally kids are more attentive than adults when they see something they are interested in. A child is more likely to remember important details and then recall them from memory than an adult, whose mind is slowly deteriorating and he may forget relevant details.