Section 21. Disqualification by reason of mental incapacity or immaturity - Rules on Evidence

(a) Those whose mental condition, at the time of their production for examination, is such that they are incapable of intelligently making known their perception to others;

(b) Children whose mental maturity is such as to render them incapable of perceiving the facts respecting which they are examined and of relating them truthfully. (19a)