I am planning my son's 9th birthday party. We are having it at a local movie theatre. It will be a private screening of Shrek 2 with unlimited popcorn and soda for all guests. This our first non home birthday party and I am afraid of getting stuck paying for extra guests ( I read another thread here about that topic). Would it be tacky to put on the invitation that if parents or siblings wish to attend the movie that they would need to pay their own way ($7.00)? If it would be okay to put that, how should I put it? Or should I just pay for everyone if additional guests show up?