My 7 year old son was very much into Harry Potter. Rather than have a Harry Potter theme party at home, he wanted his birthday party out like all of his friends.  We decided to combine this theme with bowling, and came up with the party idea for "Harry Potter Goes Bowling." Our local bowling alley did not supply invitations (although many do), so we purchased bowling party invitations at the local party store, indicating our theme in the upper corner. We purchased one wizard hat, which we also used as a sorting hat. We had a rather large group of 7 year old boys (17, including some siblings). We had 4 lanes at the alley, with bumpers to prevent gutter balls! Before the party began, I divided the guests into the houses at Hogwarts - Gryffindor, Slytherin, Ravenclaw, and Hufflepuff, and kept this a secret.  When everyone arrived at the bowling alley, I distributed Harry Potter glasses (to be worn during the party and later taken home), and lined the kids up single file.  Pretending to be Professor McGonagall, I told them the "House" names of each lane, then I put the wizard hat on each and whispered their "house assignment" in their ear, and sent them to their lane to await their teammates.  Younger siblings were put together on a team of 5 people. Each member bowled their own game, but the combined score of the team members was used to determine the winning house. They were given specific instructions on behavior and bowling etiquette, and told that if someone on their team was caught breaking one of the rules, their house would receive a penalty and would lose points. This worked like a charm. Hot dogs, chips and soda were provided by the bowling alley. We purchased a Harry Potter sheet cake from a local store. The bowling alley party package included passes for a free game of bowling, which I used as a prize for each member of the winning house. Of course, each member of the other houses also got a free game certificate as a consolation prize.  In addition to the glasses and game pass, party favors included a sorting hat key chain for their backpacks, Harry Potter stickers, and a small bag of assorted Bertie Botts' beans (jelly beans).