I would think they are around B. 11 years old
Well, not in the development as it would have happened otherwise: the whole American civilization, many people and life style was wiped out., Africa was also suffering from all the slaves taken from it. Only the Europeans profited.
From the point of view of the natives: not.
From the point of view of the Europeans? yes.
From the point of view of the Africans? not.
Personally? I am a great fun of American languages and, and I wish they were better maintained and I think slavery is a prize to pay for anything. No, I don't think it was a positive change, not with all the deaths and suffering.
Depending on the research you find, it could vary. Explain to them that while watching TV is not an "evil" thing, it can have some affects in the youth. Tell them how it can affect the behavior with friends, family and other people whom are around them. In addition you could even as far as mentioning academic success and failure.
