My son wanted a Scooby Doo party for his third birthday. I thought long and hard; I wanted to design a mystery but needed to keep it on a preschool/elementary level. The following is what I came up with. I hope this will help others!   The decorations are quite easy. We are using Halloween decorations including webs, bats, ghosts, cauldrons, etc. throughout the house as the mystery will take guests to many rooms. We will begin the party with hearing strange music. We assume it is coming from the music room (Will need to adjust according to the rooms in your house) and rush to discover no one is there! We inform the guests that we have heard of the xxxxxxRoad (put your street or road name here) ghost who seems to cause trouble when people come over. We then decide to look up the xxxxRoad ghost in our Ghost book to see if we can find out more information. When we open the book, an old torn map falls out. We discover the xxxxxroad ghost is trying to scare us away because he does not want us to find his secret treasure. The map is torn but one clue remains:    "There is a ghost in the room of play, knock him down and he'll show you the way!" We rush to the playroom where we find a ghost piñata. The kids knock it down and many smaller ghosts come out! (These are made by taking dum-dum lollipops and covering them with coffee filters. Use a twist tie around the "neck" area and draw circle eyes and mouth on the head area. Very cute and easy to make.) The next clue also floats out.   "Mashing monsters is what it is all about, go have fun and twist and shout!" We rush to the Family room where the "Monster Mash" is playing on the stereo and we dance. While we are dancing, a ghost flies down the stairs (which are behind us) drops the next clue and floats back up. (Plastic ghost from Halloween with string attached and person upstairs maneuvering.)    "Go to the place where you would dine, look under the placemats for another sign!" We rush to the dining room and discover a huge paper jigsaw puzzle. When put together we discover a picture of a girl's room (Take a picture of the room, scan onto computer and enlarge, print and make jigsaw shapes) with the next clue:   "In a little girls room there'll be lots stuff. You can make ghosties, it won't be tough!" We then go upstairs to our daughter's room where supplies for making ghosts  are laid out. Pillowcases will be partially stuffed with pollyfill to form a head. The neck area will be tied with a ribbon. Then faces will be drawn on head area. Some may want to make theirs "girl" ghosts by adding hair clips to top point of head or adding blush to cheeks. On an extra pillow case is the final clue:   "With so many ghost friends to help you out, you're sure to solve this mystery, no doubt! Go back to the place where you began and discover the treasure, I know you can!"  We rush to the playroom where we discover a treasure chest filled with a variety of small prizes and goodies. We also see the ghost!(My husband in sheet!) The ghost reveals his identity and wishes the birthday boy a Happy Birthday!  We then eat the following"   Scooby Snacks (Chicken Nuggets),Putrid Punch(a Halloween recipe that looks nasty but tastes great let me know if you want it!), plastic hand gloves with candy corn fingernails at tips and stuffed with popcorn(Only for those old enough of course!), a cauldron filled with dip placed on pretzel rod logs and red and yellow pepper flames, Frankenstein monster Jell-O rectangles, the classic graveyard dirt cake decorated with tombstone cookies and Scooby characters hiding behind tombstones, etc.    Using Halloween decorations and food really helped with Scooby. I couldn't find Scooby ideas ANYWHERE so I hope this helps others. If you'd rather, you can use a Scooby cake pan as Wilton makes one of Scooby's head. I just wanted something a little more dramatic.