Section 60.20. §s of evidence; testimonial capacity; evidence given by children

1. Any person may be a witness in a  criminal  proceeding  unless  the
  court  finds  that, by reason of infancy or mental disease or defect, he
  does not possess sufficient intelligence  or  capacity  to  justify  the
  reception of his evidence.
    2.  Every witness more than nine years old may testify only under oath
  unless the court is satisfied that such witness cannot, as a  result  of
  mental  disease  or  defect, understand the nature of an oath. A witness
  less than nine years old may not testify under oath unless the court  is
  satisfied  that  he  or  she understands the nature of an oath. If under
  either of the above provisions, a witness is deemed to be ineligible  to
  testify  under  oath,  the witness may nevertheless be permitted to give
  unsworn evidence if the court is satisfied that  the  witness  possesses
  sufficient intelligence and capacity to justify the reception thereof. A
  witness  understands  the nature of an oath if he or she appreciates the
  difference between truth and falsehood, the necessity  for  telling  the
  truth,  and  the  fact  that  a  witness  who  testifies  falsely may be
  punished.
    3. A defendant may not be convicted of an offense solely upon  unsworn
  evidence given pursuant to subdivision two.