For my daughter's 4th birthday party, we had a mystery to solve with Scooby Doo, whom she was madly in love with. Invitations were Scooby Doo that you can get anywhere. Because the party is a mystery-solving event, timely arrive of guests is crucial and should be noted on the invitation.  After each guest arrived, both boys and girls ages 2 to 7, the gifts were left by the front door, easy access for the "thief".  The children went to the kitchen where they made their own pizza, one of Scooby Doo's favorite foods.  To make this easy, I prepared pizza crust from the refrigerated section of the supermarket into about 4 inch circles or thereabouts on aluminum foil with plenty of excess.  I rolled up the edges for stability. I added some Boboli pizza sauce on each. There were bowls of cheese and pepperoni on the table for the kids to dig in and make there own.  In one of the cheese bowls I hid a traffic sign.  The child who found the sign was advised it might be a clue and to hold on to it. I wrote each child's name on the aluminum foil and baked the pizza's. In the meantime, my husband and taken all the gifts and put them in the trunk of the car.  When pizza's were being put in the oven, we asked the kids if they wanted to open presents and they all ran to the door where they left them, only to find them gone. Must be a mystery??  While my husband was loading the car, he also hid dog bones in the front yard.  Each kid was given a "bucket" and started with the youngest to the oldest.  They were to each find 3 bones, that is how many we hid, you can do whatever you choose.  One bone had a key tied to it.  When they all came back, the clue was announced to everyone and that person received a little "prize". Off to pin the bone in Scooby's mouth. I used a bedroom decorating kit I purchased at a discount store that included many Scooby's and bones. I placed them on the wall and pre-labeled each bone with a child's name. Whoever, got the closest, received a prize which was a car wheel, another clue??  Then a quick game of musical chairs for activity and again the winner received license plate, another clue.  The clues were reviewed one last time and almost everyone figured out it was the car. The gifts were brought in and opened with the bearer of the gift giving it to my daughter and a perfect photo opportunity for me.  By now, the pizzas are out of the oven and cooled so time to eat. Then of course, we had Scooby Doo cake, made by a friend, and Scooby Doo ice cream. The standard "goodie bags" were distributed at the end.  This was a great party as my daughter wants to have another one.  It moves quickly so being organized from the beginning is essential as well as having a thief who doubles as the oven watcher on the baking pizzas.  Cost was less than $100.00 for about 12 children.