This was a Harry Potter Birthday Party for my 3 yr old son.  I first bought the Hogwarts Invitations and I inserted a little letter to each child stating  that Madam Malkin was away on vacation and ask each child to design  their own customs. With a special prize given to each child that  dressed up.  Their prizes were the start of their goodie bags. (which  were purple and black gift bags with purple and black tissue paper) I  placed Harry Potter glasses and lighting bolt tatoos in them for the kids to put on once they arrived.  I also gave them a run down of the birthday activities: A shopping trip down Diagon Alley, Then the sorting hat  game, A sorcerer's stone treasure hunt (for the older kids), an dinosaur egg hunt (for the younger kids), and a broom race. I told them to meet at Platform 9 3/4 with their passwords, "Harry Potter".  That was  sure to get them excited. With the weather still nice I decided to hold  the party outside in our car port.  I blocked off both entrances with card  board boxes leaving a small tunnel to crawl threw. Then I covered them with sheets to make it really dark (plus to make it look a little  nicer).   I them put a platform 9 3/4 sign over the tunnel entrance. I took white poster board and drew the school house symbols on them and colored them to match. They looked great.   With it being close to  Halloween I was able to get orange and purple lights to hang around the carport to add some mood lighting. I purchased some Harry Potter  decorations to complete our themed area.  I also purchased the Nimbus 2000 broom and hung that up as well.  In addition to the  school sign I also made a black and gold banner that said "Happy Birthday ------" using the letters like Harry Potter's name.  It turned out great. I hung plastic bats and short pieces of streamers from the  ceiling to add to the effect. The room kind of look like the dinning hall in  the movie.  I set up two long table and set a place for each child. At there place setting was a plastic Harry Potter party cup with there  names on it (so they could take them home-party favor), A Harry Potter plate, napkin, purple and black silverware.  There ware also gold  gobletts  (party favors-Birthday Express). The tables were dressed with purple and black table cloths, Harry Potty confetti, silver and gold star confetti and plastic snakes.  I also turned our upstairs hallway  into  Diagon Alley. When all the doors are closed the hall becomes very  dark which worked perfect. At the bottom of the stairs I made a sign  that said "Diagon Alley" with a arrow pointing upstairs.  At the top of the stairs I hung  up a sheet, behind the sheet was my son's play hut that I had set up for the kids to crawl threw which became Vault 687 at  Gringott's Bank.  At the end of the tunnel was a basket with plastic gold coins. Each child got to get two. At the other end of the tunnel they  would crawl out and begin their shopping trip. First was the Owl  Emporium. I had white owls set up in a display (bought the owls from Birthday Express). Next was Ollivanders-the wand shop. I made wands out of wooden dowls. I painted them black and used other  colors to paint lighting bolts, moons, starts, clouds, ect..., then I wrap  the bottoms (the handles) with gift wraping ribbon.  I used red, yellow, purple and dark green. Each wand was unique just like each child. I  placed them in neckless boxes that I got from the local jewerly store.  I set up the wand display at the end of the hall and placed signs next to  each shop. When the children arrived for the party  my son and I  greeted them dressed as Harry Potter and Professor Magonagal. We asked each child for their password and gave them their goodie bags,  then we took them into the house and up to Diagon Alley.  I had one of  the parents to help me with the shopping trip.  Because it was dark I  had bought plastic old fashion looking laterns that ran on batteries to  lead  the children throw Diagon Alley.  The kids were so excited and thought it was so neat.  My son was total thrilled. Next we took the kids outside were they entered the carport/dining hall. The kids were  amazed and so excited when they crawled threw the tunnel into the  newly transformed room.   They all took their seats and we began the  sorting hat game.  I had a friend hiding with our baby monitor in another  area.  And the speaker part of the monitor hiding near the sorting hat chair. So when we put the hat on the kid it sounded like the hat was  actually talking to each child.  Each of the kids got sorted into the four different houses.  (My friend did a great job and sounded just like the  sorting hat on the movie) I gave them each a school symbol that I had  made to pin on their custom. These would also be the groups used for the treasure hunt. So after that we began the Sorcerer's stone treasure hunt.  I sent the kids all around the neighborhood.  Each stop was tied  into a theme from the movie. For instance the woods by our  neighborhood happens to be right next to our elementary school as  well,which has path threw it. That was used to symbolize to the Dark Forest. Which was a perfect place to have a clue.  We also had a pond  near which symbolized the pond in the beginning of the movie that they  float across to get to Hogwarts. The neighborhood playground was  symbolized as a Quiddith field and the bus stop as the train depot. An example clue:  By Hogwart's there is a place a very DARK place were Harry is sent with Ron, Hermione, and Malfoy to serve detention.  Hagrid leads them down a path to get there. So detention has been  serverd to you, can you find your next clue?  (Answer:  The path in the woods next to their school) The final clue lead them back to the party were I had hidden a red glittered painted rock in a storage shed with a  beware of fluffy sign on it.  Even though my son was only three there  were several school aged children at the party so were had to accomadate for them. My son wanted to go with the big kids and actually had a great time. I did send an adult with each group to keep an eye on them plus to help them out if they got stuck on a clue.  While the older kids were out doing the treasure hunt I had the younger kids do the dinosaur egg hunt in the backyard.  Which were easter eggs  painted to look like a dinosaur eggs and filled with candy. As prizes for  the treasure hunt I had two of each (because there were to kids in each  group): an address/date/favorite activities book that was very cool (found at a local bargin store), Bertie Bott's Beans, Harry Potter stickers  and the two plastic laterns that we used for the shopping trip down  Diagon Alley. As the kids arrived from their treasure hunt they got to  pick their own prices.  Which work out great! After the treasure hunt we  sat down for a little refreshment of cake and ice cream. The cake was made out of Harry Potter toys. We had purchased the castle (small in size) and the small tree with the car from the toy store. We had a local bakery place the castle, tree and car on top of the cake along with a H.P. candle. It turned out so neat. Another good idea: for ice cream buy  the ice cream that is in the little cups and just pass them out.  It saves  time and money. After cake and ice cream we had a wizard hat pinata (also from Birthday Express) for the kids to all take a hit.  While the kids  ate their candy from the pinata.  My son opened his present.  Then we had the broom race so the kids could get their sugar highs taken care of.  The party was a HUGE SUCCESS! The kids and parents talked  about it for weeks.