I think knowing about the adoption earlier is better for an adopted child. And the time will be 6~7 years old because this age kid = at this ages, kids can understand the concept about family and adoption. Sometimes parents who adopted a child did not want to hurt their adopted child. Therefore, they postponed the time to talk about it. Even they missed the chance to talk. However, the truth that he/she was adopted can not be hidden forever. This just make the situation getting worse = to get worst. My point is that an adopted child will get shocked as much as the amout of time that they hide about the adoption. Also, If he/she know that the child was adopted earlier, they will live and behavior differently. But this does not means = mean that the child become a bad person. Because they will appreciate that their parents choose him/her. After they know about it, they will give more love to their parents not like the past when they just receive love as they didn't know about the adoption. So knowing about the adoption even if the child was young have positive effect for their lives.