Birthday Party Planning

The girls said the funniest thing today. They asked where we were having their birthday party. I explained that we just bought them a stupidly expensive birthday present. Their birthday party was going to be in our backyard.
They tried to argue the party location, but I wasn't interested in the conversation. They received the present of their dreams. They would have to figure out how to manage a home party.
Shortly after we were sitting with pens and papers plotting the big event. They decided to invite everyone over to play games. We asked our neighbor if we could use her yard. Her house sits on a double lot, so we wanted to take advantage of the space to put a volleyball net. She said yes and the party planning continued.
At some point we decided to invite Erin to put her name on the invitation. Erin has the same birthday as the girls, although they hadn't thrown a joint birthday party previously. It made sense, though, to bring it all together as they share most of the same friends.
I kept bringing down the plans to things that didn't cost as much as they wanted to spend. I was still recovering from the iPhone invoice.
In the end we planned a really fun party and twenty middle school girls received invitations. As I typed that last sentence, I realized that I must have lost my mind. Twenty middle school girls?