We have no reason to think “more interesting results” is what made children helpful in the experiments. What matters is whether the thoughts children have about the phenomena are direct or a product of inference; how interesting the results are is a separate issue.

We have no reason to think this is supported by the passage. The psychologists believe adults are more capable than children at identifying their own thoughts. So the passage actually suggests that adults might be less likely to give inaccurate reports of their thought processes.

The author never suggests that adults are “infallible” (make no mistakes) in access to their own thoughts. Although they’re better at identifying their own thoughts than children, this doesn’t imply they make no mistakes in accessing their thoughts.

Supported, because the psychologists were trying to study whether people know their own thoughts directly or through inferences. Since the psychologists believe adults are better at identifying their own thoughts, children would be better to study because they’re more likely to make errors in identifying their own thoughts. This provides a better opportunity to examine the process of how one comes to know their own thoughts. If they can make mistakes about their own thoughts — as children do — this helps support the theory that we know our thoughts through inferences. Had adults been used instead, then we’d have less opportunity to see a potential mismatch between the adults’ thoughts and how they describe those thoughts.

The experiments involved examining children’s own thoughts, not their ability to infer the thoughts of others.