Final answer:
Children begin to develop a keen sense of danger around the age of 5.
Step-by-step explanation:
Children don't develop a keen sense of danger until around the age of 5. At this age, they can catch a ball thrown from a meter away, balance on either foot for about ten seconds, and demonstrate good control with a pencil or marker. They begin to color within the lines and can reproduce many shapes and letters. Some children may already be learning to ride a bicycle with training wheels. Therefore, among the options provided, age 5 is likely the earliest age at which some children may start developing a basic sense of danger, but it's an ongoing process that continues into adolescence and beyond.