Kuhn, D., & Pearsall, S. (2000).

Developmental origins of scientific thinking. Journal of Cognition and Development, 1, 113-129.

In a study of 4-6-year-olds, Kuhn & Pearsall, 2000 investigated whether children of this age were sensitive to evidence as a source of knowledge to support the truth of a claim, distinguishable from theory that enhances plausibility of the claim. Participants were shown a sequence of pictures in which, for example, two runners compete in a race. Certain cues suggest a theory as to why one will win; for example, one has fancy running shoes and the other does not. The final picture in the sequence provides evidence of the outcome -- one runner holds a trophy and exhibits a wide grin. When asked to indicate the outcome and to justify this knowledge, 4-year-olds show a fragile distinction between the two kinds of justification -- "How do you know?" and 'Why is it so?' -- in other words, the evidence for the claim (the outcome cue in this case) versus an explanation for it (the initial theory-generating cue). Rather, the two merge into a single representation of what happened, and the child tends to choose as evidence of what happened the cue having greater explanatory value as to why it happened. Thus, children often answered the "How do you know [he won]?" question, not with evidence ("He's holding the trophy") but with a theory of why this state of affairs makes sense ("Because he has fast sneakers"). A follow-up probe, "How can you be sure this is what happened?" elicited a shift from theory-based to evidence-based responses in some cases, but, even with this prompt, 4-year-olds gave evidence-based responses on average to less than a third of the items. At age 6, confusions between theory and evidence still occurred, but children of this age were correct a majority of the time. A group of adults, in contrast, made no errors.