Choose one best prenatal, infancy, toddlerhood, preschool age, middle childhood, adolescence, young adulthood, middle adulthood and late adulthood

Preschool age because it's the time where you learn more about things like numbers, letters and how to socialize with others.

The truth is that any source can be the best source for some kind of research. as an example, if you were to write an essay about the credibility of wikipedia, would you avoid citing wikipedia? clearly not. as we know, the president of the united states jumps on twitter all the time. if you’re writing about trump, what better source can there be? it is, quite literally, an original historical document. the same would be true if you were writing about the events of the moderately recent revolutions in egypt and syria. what better source than someone who is right there in the thick of things? clearly you would have to contextualize the source as at least moderately unverified in most such cases.