We're going to be playing a bunch of games outside for the afternoon, and we're going to get messy! Don't worry, at the end of the day, we're going to wrap it all up with a water fight to clean off.
Wear a bathing suit under some clothes you don't mind getting messy or possibly permanently stained or wrecked. Things could get a little nuts.
In case of bad weather, we'll play non-messy games inside.