Here's what we did...
Most of the decorations were in the form of props for the kids to use and eat or play with during the party and then take home as favors. Although I did make the "brick" wall for platform 9 3/4 as well as a set of house banners. We also used our Harry Potter books as decorations.
Of course every themed party starts with a fun invitation. These are the invites we sent, most of them hand-delivered to the kids at school. (Click here for details about the invitations and links to all the resources I used.)
I met all the kids (12-2nd graders, plus my kids) in front of the elementary school when school was over. They were each handed a Hogwarts Express ticket.
Then it was time for potions class. We had four different "potions" experiments set up around the room for the kids to try.
Then my husband (the potions master) did some advanced potions for the kids.
Then we headed off on foot again to a little church building right behind our house where we had the rest of the party set up.
We had house tables set up there too. Once all the kids were settled, we had potions books and wands ready. Each child got to choose their own wand, and the kids got to practice casting spells from their spell books. (Click here to see how to make the wands.)
For the "birthday cake" we had Cauldron Cakes and Golden Snitch Cupcakes (tutorial here).
Instead of having all the kids bring presents, we just asked each child to bring a wrapped book for a book exchange. Each child brought a book and then each child got to go home with a book. They also each got a Hogwarts Library Bookplate (follow link to print your own) to put inside their new book.
I had also brought a wizard robe and other items for the kids to dress up as a Hogwarts student and have their picture taken for a photo booth...but the camera died in the middle of the party and we ran out of time anyway...so Katie will just have a really fun Hermione costume to wear next Halloween.
Whew...It was a lot to put together, but the kids had a blast. I'll be getting up tutorials and/or links to where I found the ideas in the next week or so. If there's on aspect of the party, you're especially curious about, let me know and I'll to do post about that part first.
I have lots of Harry Potter inspired gifts and fun things in my shop. The selection is always changing.
See these links for more details about other Harry Potter themed crafts we've done...and be sure to check back because I'll be adding more as I get them written up.