It is called defamation or slander if your adult child is intentionally spreading false and damaging information about you to others. Defamation is the act of making false statements that harm a person’s reputation or standing in the community. Slander specifically refers to spoken defamation.
If the false statements are communicated in writing, it is known as libel. In any case, such behavior is not acceptable and can cause significant emotional distress and damage to one’s reputation.