Ruling
      on kissing daughters or sons on the mouth
Question

                Is
      it true that a father should not kiss his daughter on the mouth and that a
      mother should not kiss her son on the mouth?
Praise be to Allah.This
      is true. A man should not kiss his mother or daughter on the mouth.
      Similarly, a brother should not kiss his sister on the mouth, or his
      paternal aunt or his maternal aunt, or any of his mahrams. Kissing on the
      mouth is only for husband and wife. And Allaah knows best.