There were supposed to be 13 kids at the party. One pulled out at the last minute (her Mom felt that it would be "too scary" for her).
The first activity was Wand Making. As everyone arrived, they were given a 12" wooden dowel and directed to a table containing glue, glitter, feathers, paint, and other assorted items.
Once everyone was there and the wands were put up to dry, we started the Snitch hunt. We had taken Styrofoam balls and spray-painted them gold. We learned quickly to do a light first-coat to seal them or the paint would eat the balls (I hate when that happens, don't you?). After adding two white feathers, we had Snitches. We hid them around the back yard and each kid was told to find one and put it with their wand.
Potions Class was next. Kids paired up around a big table. Each was given a big bowl. I went around filling them with warm water from a big Thermos jug. When a kid asked, I said "it's magic Dragon water." They laughed until one kid stuck his finger in, pulled it out with a yelp and said "he's right, it's really hot." Everyone else had to test it and soon they were completely enthralled. Everyone took a couple scoops of Borax (I called it something like "ground-up Unicorn horn") and stirred. Then I poured in a bunch of white Elmers glue and added a couple of drops of green paint. This gave the kids a watery mess. Gak is a super-polymer with strange behaviors; when at rest, it relaxes into a thin ooze. But, when you stir it, it binds up. The harder you stir it, the tougher it gets. A couple of the kids screamed the first time they started stirring because some "magical" force pulled the spoons right out of their hands. One boy stirred so hard that his gak turned almost solid and snapped his spoon in half. Months later, kids were still talking about the Potions Class
We packaged up the gak for sending home and sent the kids to Charms Class. We gave them back their wands (hint: glitter-paint takes forever to dry, avoid it) and put a chocolate frog in front of each kid. They practiced their "swish and flick" and assorted magic words trying to levitate their frogs. Finally, We said "these must be non-magic frogs, why don't we help them," picked one up and popped it into our mouth. The kids all did the same.
History of Magic class was next. We read them a couple of Halloween books while I got the food ready.
We had a Feast with pumpkin pasties and giant fingers (little hot dogs baked in dough).
By then the Magician had arrived. The kids sat on mats while he entertained them in-front of the castle. He did a great job and involved the kids in most of the tricks.
The last class of the day was Care of Magical Creatures. We made owl puppets based on a design we had seen being made at FairytaleTown. We pre-cut all the pieces and let the kids assemble them and clue feathers on.
After cutting the Harry Potter cake purchased from the local supermarket (I came to my senses before I started making a castle cake from scratch), everyone headed inside for gifts and goody bags. The bags contained another chocolate frog, gold coins, snakes, and stickers.
Of course, as everyone was leaving one parent looked around the yard at the decorations and the remains of the activities and asked "do you realize how much pressure this is going to put on me to make MY son's birthday special?"