There are days when I feel that I have the strength to organise a paint/glue/sand/water activity for the children. But wisdom reminds me NOT to get it happening unless I judge I have to strength to clean up afterwards as well.
Recently, I decided I had the fortitude to get this activity going and to clean up at the end. We road-tested Woody's new birthday sand and water play table, and it was good clean (but not dry) fun. I filled both sides of the table with warm water and I made one side bubbly as well.
It's best if you set up an activity like this with the full expectation that each item of clothing will go straight in the wash when finished, and that both children will go straight from the yard to the shower. Possibly naked.
That way, you can allow them to enjoy the experience without getting on their case every thirty seconds, nagging them to keep clean or dry.