How do I prepare my kids for their first sleepover? What should I do if they want to come home?
On the parent side:
Talk to the host parents to make sure you know what the plan is. Will there be a party? Games? Pillow fights? Food? Candy? Bedtime rituals, bath, brushing teeth, prayers? Are there house rules? Get a guest list so you know what other kids will participate (are you okay with who is on the list?). Make sure you agree with the plan.
Also, agree with the host parents what to do if things don't go according to plan. At what stage do you want to be contacted? How bad are things allowed to turn before you want to pick up your child? Is there a "point of no return": at what time of night is the stay committed and the child must stay there? What are the host parents' plan in case of a real (medical) emergency?
On the child side:
Talk to your child about what they expect to happen. What do they want to happen (like activities)? What to they not want to happen (like bed-wetting)? Make sure the child understands what is allowed and what isn't, and what kind of situations qualify for being picked up in the middle of the night. Make sure that the child is comfortable with the host parents (they might have to soothe the child, and this had better work), and if the child is comfortable with all the other guests.
Expectations can be big, and even a successful sleepover might not be a happy one if some detail went badly. Try to steer the child's expectations; not too high, but still a fun event to look forward to.
Try to make the child grasp the most difficult thing: Understand that it won't be perfect, and no matter what happens, always try to make the best of it and enjoy the good bits.
We began preparing our kids for sleepovers by starting with late nights out. They would stay at a friend's house until a specific time and then come home. After a few repetitions, my kids would usually ask to stay over for the night. We found that starting slow and expanding was easier for the kids than being overwhelmed with the thought of an entire night out.