Dd1 was about 14 months for her first sleepover at my folks. When DD2 was about 2, so dd1 3, they both started fairly regular sleepovers with my folks. They love it - Mum makes pancakes in the morning, and the rules are stretched a bit more at home but nothing I'm not comfortable with. DH and I get valuable grownup time together knowing the girls are safe and happy. My fks love it too. Not happy for them to stay with anyone else yet - family or friend. A couple of DD1's kindy friends have sleepovers now at age 5 but that is waaaaay too early for me.