Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "When children reach seven years of age, command them to pray; and when they reach ten years of age and do not pray, punish them; and separate their beds. And when one of you marries off a slave or a hired worker, then let her never look at the area from his navel to his knees, for from the navel to the knees is awrah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3233