Solve The Mystery
Create a mystery for kids to solve, scavenger-hunt style. For example, say a ghost has stolen all the party treats, and now the kids have to find them. Leave notes with clues around the house that will lead to the next clue. The clues can be riddles or jokes that will lead the kids to another clue, with the mystery finally culminating where the "ghost" has hidden the treats.
Scooby Snack Game
Part of every Scooby-Doo story concerns Scooby's endless appetite, especially for something called "Scooby Snacks." Have kids take turns dropping Scooby-Doo graham crackers or Scooby-Doo fruit snacks into a wide mouthed jar. Give everyone a set amount of crackers or snacks and see who can get the most in. To make it even more challenging, or for older children, blindfold the person who is playing to see how many snacks they can get into the jar without seeing anything.
Matching Clues
Make up a matching game where kids have to guess who said what. On one side of a piece of paper, list Velma, Fred, Scooby, Shaggy and Daphne. On the other side, list things that each character says, and let kids draw a line from the character to the saying. Scooby always says, "Ruh roh," while Fred's catchphrase is "Let's all split up and look for clues." Shaggy is most likely to say "Scooby-Doo, where are you?" Velma's favorite saying is "Jinkies!" and Daphne's line might be "Would you do it for a Scooby snack?" Include a villain to be matched with the phrase "I would have gotten away with it, if it weren't for you meddling kids!"
Who Are You
This game would work for very young children. Print pictures of the Scooby gang from the Internet. When guests arrive, tape a picture of a Scooby character to each of their backs. Have each child ask questions about the photo on their back to try and figure out what Scooby character she is wearing. For example, the child might ask if she is wearing glasses or not. This game can go on until every guest figures out which person, or dog, she is.
Pin the Tail on Scooby
This game is appropriate for young Scooby party guests. Draw and color a picture of Scooby on a piece of poster board, or print one off of the Internet and have it enlarged. Draw enough small tails on brown construction paper for each party guest. Cut out the pieces and stick a piece of double-sided tape on each "tail." Put a blindfold on each child and have them try to stick the tail to Scooby as close to his real tail as they can get.