Shemiras Halashon Halachos

Hilchos Lashon Hara chapter 9, section 5

Even if one hears one's young children speaking lashon hara, it is a mitzvah to rebuke them and stop them as it says, Educate the child according to his way (Proverbs 22:6). As the Orach Chaim (343:1) explains, this applies to all Torah prohibitions.

Hilchos Lashon Hara chapter 9, section 6

If someone told someone something, he may not repeat it to others unlike the person gave him permission and that is only if it is not lashon hara.