I was asked to organize an impromptu Treasure Hunt/Scavenger Hunt for the local kids ranging in age from 7 to 12.  I reckoned on two teams of mixed ages and used some garden pegs that I had (but just about anything can be used) on which I wrote various letters and numbers with a black marker pen.  I placed these markers at strategic locations in the front and back yard, and then composed clues to lead from one marker to another. I varied the use of numbers and letters so the pegs weren't in a sequence so it didn't matter if one team stumbled on a peg that they weren't supposed to. I had all the clues on pieces of paper in envelopes which I kept, and when the team came and told me which peg they had discovered, I gave them the clue for that peg which led them to the next peg. The pegs were hidden under easily identifiable markers such as colored flowers, bushes, shoes that I put out, garden ornaments etc. I started the Hunt by giving each team a giant letter which I had cut up and asked then to reassemble it. Once they had performed this task, each team got a magic staff (a long pole possibly the handle of a garden tool or similar), and occasionally they had to use that staff to measure from one peg to another in certain directions (say 2 staff lengths towards the tree, then three staff lengths towards the house). I would also throw in the occasional puzzle such as a spot the difference which they had to solve in order to get the next clue to get to the next peg.  I started off the teams at either end of the peg trail, so whilst I could use the same set of pegs, I had to have two sets of clues.  Eventually, the teams got the final puzzle which was the traditional hen, grain and fox puzzle.  As we have a pool, they actually tried to solve the puzzle by swimming across the pool with pieces of wood that I had marked as either the fox, the hen or the grain.  It kept the kids busy for a long summer afternoon, didn't cost very much to set up, and taxed my brain for a few hours when I composed the clues in rhyme!