Be the first to find the object making noise wherever it is hidden.
Record some noise onto a cassette based on whatever the theme of the party is. For a pirate party use the tick tock of a clock. For a train party use a train whistle sound etc. Put about two minutes of the sound onto a tape. Then when the game starts mount an appropriate picture to match the theme on the tape deck and hide it somewhere. Turn the volume load enough so the kids can find it. First one to find it wins a prize.