You asked

How do I make sure to throw a good slumber party?

Kids shouldn’t be too young.
Children should all be at least eight years old before attending a slumber party. Younger kids often require way too much supervision.
Don’t invite too many
This is definitely one time when you don't want to invite the whole class.

Four is a nice number. Six may be manageable for very, very special sleep over occasions.
Keep even numbers.
One may be a lonely number but three is a squabbling number. Particularly with girls, four will mean that no one is left out.
Don’t let the party go on too long
Begin the party at dinner time and end it at breakfast the next morning. Any longer is at your own peril!
Master parent-to-parent communication
Be sure to call the parent of the invited children. Let them know what to pack (things like a sleeping bag, a favourite pillow, PJs and a toothbrush); what time to drop the child off; and what time to collect her the next morning.

Give the parent an idea of the scheduled activities so they know what clothing to pack.

If you plan to watch a 12A movie, make sure to clear it with the other parents and make sure to preview the movie as it may be unsuitable.

Make sure you have the parent's mobile numbers in case you need to reach them during the night.
Plan activities
While you don't have to have every minute of your child's slumber party scheduled, it’s good to have a general plan so the kids don't turn to their own devices or get bored.
Make a slumber party menu
Provide plenty of kid-friendly, healthy party foods in advance. Leave nothing to chance  as kids get hungry, especially near midnight.
Schedule lights out
Set a time for lights out well in advance. Plan more sedate activities for the hour or two before bedtime, such as a movie, to get the kids to dial down to a level where sleep is a realistic possibility.
No texting or calls.
Don't allow the kids to text or e-mail from their cell phones during the party, unless they want to get in touch with their parents.
No electronic games allowed
Someone is always left out with these electronic games.

Discuss this with your child prior to her guests arriving and suggest more group friendly activities.

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