(slumber party heaven)
To have an indoor campout sleepover you need to have pretty much everything that you would have at an outdoor campout.
If you have a fire place you can start a fire in it before the girls come to the party girls house and have the girls lay their sleeping bags near it for the outdoor feel as they sleep.
As for decorations you would want to hang twinkle lights from the ceiling to create the 'under the stars' effect.
If you don't have a fire place, then make a campfire! All you need is a large battery powered candle (or multiple small ones) placed in the center of 'logs' or cardboard tubes wrapped in brown construction paper. Take red, orange, and yellow sheets of tissue paper and cut them into large 'flame sized' slightly wavy tiered triangles and glue them to the 'logs' to form a 'campfire'.
As for food if you have a fire place and older girls over if you feel comfortable and are monitoring the girls at all times they can roast hot dogs over the fire. If you aren't comfortable with that you can always grill them while the girls play games or chat. S'mores is also great if they can use the fire place. Other food ideas are chips and dip, fruit and veggie trays, and do it yourself ice cream sundaes. Remember to have snacks constantly available for the hungry guests!
Some games to play are classic truth or dare, board games, or balloon volley ball (streamer strung across a room and two teams of girls who play volleyball with a balloon.
I hope these ideas can help you have the best indoor campout ever!!