I do alot of theme parties but I think my favorite was the backwards party I had when my oldest son turned 10 years old.  We mentioned on the invitations that the party was a backwards party and asked the kids to wear their clothes backwards. When they arrived we opened up the gifts. After, we ate cake underneath the table. The cake was not decorated, it was just plain. The icing and candies were in containers for the kids to decorate it themselves.  They loved that part. After we had cake we sang "Happy Birthday" and then we had hotdogs and chips. We played games like backwards egg toss & backwards sack races. The kids had a great time.  This idea worked so good because at age 10 the kids were thinking they were too "old" for a party. This theme worked great for their age!!