If you know that there will be a large number of kids attending your party and you cannot afford any more kids in terms of both your budget and/or space limitations, it is best to proactively write in your invitations that no other guests can be accommodated for this party. This is something you should do if you anticipate that parents will want the guests’ siblings to also attend, and you do not want to consider them attending due to your party plans. In this case, the clearer you can be with the kids’ parents the better and the earliest notice is also the best, and that begins with receipt of the invitation.
Use language that is clear, and explains the reason why. As an example, “Due to the large number of kids being invited to the party, no extra guests will be accommodated, including siblings.” This way people understand the reason, and you will not have to have the conversation over the phone when the parents RSVP or have the party guests show up with their siblings at the party door ~ when it will be incredibly awkward to not allow them to attend as well.















