I strongly support the idea that a person's childhood years are the most important period of a person's life. Because the childhood of one humanbeing form his personality and is the easiest time to take many stuffs, which is not possible to learn when people are being adult, into his brain.
Many studies which were taken by scientists show that it is easy to learn anything when people are young. For example, It is very important to can speak another language in these days, and the childhood years of people are perfectly suitable to learn language. There is a friend of mine who can speak English and Korean well, she spent four years at the united states when she was six-year-old girl. Because she learn another language in her early age, she get a lot of benefit when she want to have a job.
Furthermore, the childhood of people is important period to form their personality. For example, We frequently have seen the news about criminals that turned out they have bad memories in their childhood and they affect their character and make them do things which is against the law. In addition, I often have one friend who also has bad memory about his elementary because he always had problem to interact with peers and other friends didn't play with him. As a result of that memory, he still has hard time to meet a new person.
For these reasons, I think a person's childhood period is the most crucial time to build his or her character because it affect a person's future life. And it is the easiest time to get anything into his brain because very young child can learn two languages simultaneously.