(I did this one over one year ago, when Pokemon was just becoming popular. So there was very little stuff to find.) This idea will mostly require your knowledge of Pokemon, your children will want to help!  I used a puzzle I found on a website for invitations, my son printed the party details on the back. This will require the party to be outside on a summer day, you need to have a yard (a small one will do) with a sprinkler or kiddie pool.  To save money, get most of your decorations on the internet off of Pokemon websites. (a color printer works better and good paper. I cut out all I could find to place on plain red, white, or blue table cloths(plastic). Then, the fun part-decorate your yard like a mini Pokemon world. I found watching the program or reading my son's books helpful. I found clearance Japanese decorations to help out, used a kiddie pool as Misty's Pond and placed water pokemon on foil cupcake cups. Also I made fishing rods to try to catch the water pokemon. My son had a tent that I turned into a Pokemon Center, with drinks and a place to rest. We also had older children acting like "Team Rocket". His swingset was turned into a carnival with streamers and Pokeballs. Each child was given Pokemon cards (2-3) but was able to "catch-em" throughout the yard, like a scavenger hunt.  What ever they find they keep. No one lost/kids liked it.