The best time to give advice to your children is while they're still young enough to believe you know what you're talking about.

The line jokes that parental “expertise” is partly a matter of timing: when children are small, they tend to accept guidance as truth; as they grow, they test, question, and compare it against peers and experience. Beneath the humor is a real observation about authority and trust—advice is most effective when the listener is receptive and the relationship still grants the speaker credibility. It also gently punctures adult self-importance, implying that parents may overestimate how persuasive their counsel is once children develop independence. The aphorism’s appeal lies in its blend of affection and irony about the limits of parental influence.