Get really dirty!
The 'Scheldestrandje' is a man-made beach consisting of squirted on sand. At ebb, when the water is low, a part of the beach becomes dry. This area then partially consists of a layer of mud.
Nice for the kids, because if they are normally not allowed to play in the mud here they are allowed!
And did ythey get a bit dirty? No problem, just rinse it off in the water or under the shower at the beach!