For many years I have been involved in running activities at events and camps for Scouts and Guides, ranging up to mass games for over 600 kids at once. In many cases these have included silly, wet or messy games which always proved very popular with the participants. However, in most cases we had to rein back our ideas somewhat due to consideration of budget, weather (some events were in cold times of the year), washing facilities or capacity, leaving me with a host of ideas not fully implemented.
After discussion with some friends, we decided to run our own messy games day, which we christened 'Messtival'. This means we could take part in the games, and they could be as over the top as we liked. The event has now been running for a few years and has been growing in popularity each time.
I do not make any claim that any of these games are completely original, and thank those people whose ideas I have adapted over the years.
This Instructable will take you through how to run a similar event- there are many ways to change it to suit your needs, but I hope it gets you started. It would be great to hear your ideas in the comments.
I won't reproduce the mess recipes here; please see my other Instructables where I have fully described them.
Gunge Recipe http://www.instructables.com/id/Gunge/
Slime Recipe http://www.instructables.com/id/Slime-1/
You will find examples of other clean games and obstacle courses at my website http://www.superpants.net/games.html
These may eventually form a new Instructable. Also on the site you will find loads more info on making mess.