My kids didn't do sleepovers until age 8.
Many of their friends did them as young as 3 (with family friends) others weren't allowed until 13.

While in kindergarden, when the offers really started coming, we did 1/2 sleepovers.
They could invite a friend over around 5p for dinner. They played games etc. until around 8p. Then everyone got into jammies, we made popcorn and put in a movie. By 10p the friend's parent came to pick them up for sleeping in their own bed.

It allowed for all the same fun without nervous children and hurt feelings at 2am.