Although not unheard of, it's rare for an adult to show up uninvited and unannounced at a grown up party. But it's much more common with kids' parties. Some of it is miscommunication and misunderstanding, a parent assumes that if one kid is invited, all the kids are invited, or doesn't know she should RSVP. Other times it's unavoidable, a babysitter doesn't show up for the younger child, or the older child's plans are cancelled and the harried parent doesn't have another option. Although it can seem like a big deal, uninvited guests are easy to handle. The best way to handle an unexpected guest is to prepare for him in advance!
Try to avoid entertainment or activities that are dependent on their being a specific number of guests. After all, it's not unusual for young guests to be unable to attend a party at the last minute. Give your entertainer an approximate number so she can plan appropriately, but don't feel like you need to give a specific number. Make sure to ask your entertainer ahead of time if his price changes based on the number of kids. If it doesn't, but you wind up with five or more extra kids that create extra work, consider an extra nice tip! If possible, buy a few extra party favors or goody bag supplies, making sure to keep the receipt in case you need to return them. If the goody bags or favors are personalized, make sure to get one or two plain ones. If you're serving cupcakes or other individual treats, make sure to have extras on hand (a good idea anyway given the likelihood that someone will drop something).
If you've asked for RSVPs and haven't received them, feel free to contact the parent and ask. This is one downside to using sites like Evites. Parents aren't always sure who you meant to include in the invitation. Paper invitations can be addressed to a specific kid. Some paid electronic invitation sites like PunchBowl let you specify who is invited to the party. If you do find yourself running short on supplies, pull your kids and possibly their closest friends aside and explain the situation (not naming names of course). Explain that in order to be a good host you need them to hold back on taking things, but that you'll make it up to them later. If an unexpected child does arrive, remember that the child probably has little control over the situation and should be treated as a welcome guest. It is however ok to say to the parent "Oh, Johnny is here, too, what an unexpected surprise" in an overly bright and perky tone, trust me, the parent will get the message.
Have you ever had an unexpected guest? How did you handle it? Tell us in the comments.