"Imam Ali ibn Abi Talib (as) said: "A woman touching her daughter in an inappropriate manner once she has reached six years of age is a form of indecency (a branch of fornication)."
Man Lā Yaḥḍuruh al-Faqīh #1295"When a girl reaches six years of age, a boy should not kiss her, and a boy should not kiss a woman once he passes seven years of age."
Man Lā Yaḥḍuruh al-Faqīh #1293Hadith.4508 - It is narrated: "Children should be separated in their sleeping arrangements at the age of six years."