Just adding to other ideas but my mom gave me children morality books I read in the bathroom and before bed. Though I think most of my morals came from star trek, batman, and thundercats.
Side story: I remember the exact moment my mom caught me stealing a ball it was not the consequences that hurt me it was my moms disappointment that lingered in me.
Different methods all none invasive but check with kit first. For example getting old tooth brush or hair from brush. Could also bring it up in conversation see how they react. Like thinking ancestry test. If they panic you know something is up.