My child has started speaking rudely and mocking others. How do I teach him to guard his tongue?

A child guards his tongue when he understands that words can hurt and when he hears kind words at home. The Prophet ﷺ said: “A Muslim is the one from whose tongue and hand the other Muslims are safe” (Sahih al-Bukhari 10). Correct mocking calmly, and explain how it feels to be the one mocked. Be the example: do not backbite or curse in front of him. Teach him to apologise when he says the wrong thing. Praise him when he speaks kindly or calms things down. A home where the tongue is gentle raises children who are gentle in speech. See educating the family.