Cheated on an exam when I was eight years old. Should I tell graduate admissions?
As noted in the comments, actions committed long ago as a child are (and should be) entirely irrelevant to graduate admissions.

It is well understood that children do not have same ability as adults to comprehend the consequences on their actions.  As a result, many legal systems wipe a child's record clean of most or all juvenile offenses upon reaching adulthood.

I would thus similarly argue that any academic offense predating your undergraduate education should generally neither be reported nor considered in an application for graduate school.