One fun activity for a kids' sleepover is to play "truth or dare." This is a game where players have to first say whether they are going to tell the truth or do a dare. Once they have announced the choice, the other players ask them questions or come up with things the player wouldn't want to do. Another activity is to decorate pillow cases.
The decoration of pillow cases allows the kids to use new cases when they are finally sleeping at the sleepover. Twister is another activity that is fun, especially when the sleepover group numbers more than three or four kids. The game is one where bodies twist over, around and through other people's limbs and torsos. A scavenger or treasure hunt is another good activity for a sleepover. The breadth and length of the hunt can be left up to the person organizing. The treasure hunt could be small and limited to the house where the sleepover is occurring. It could also be expanded to include the entire neighborhood.
For a sleepover that is only attended by girls, a game that incorporates putting on makeup is a fun activity. The object can either be serious, with each girl trying to look the best she can, or it can be silly, with girls creating exaggerated effects for fun.