Play London say;

The natural environment offers unrivalled opportunities for free play. When adults think about where they played as children, a majority usually cites a natural environment as their preferred play for play when they were young.

The natural environment also offers many types of "loose parts" to use in play, skimming flat stones over water, breaking off sticks from a bush for a sword-fight, and having a snail or slug race are just a few of the delights of play with natural materials.

Sand, water, boulders and fallen trees are all great things to leave about to stimulate play in a park or school playground. I have heard apparently sane people give the opinion that sand is dangerous for children, they are simply wrong. The beach is one of the finest natural play environments, just build a sand-boat to sit in when the tide comes in, or add a small stream flowing across it to be dammed up, and I could play all day.

This does not mean we want everyone to turn their backs on swings and roundabouts, children love them and they signify to all ages a place where children have a right to play, rather we want to add to them to preserve natural places, spaces and features, and make them accessible to all in public spaces.

Download London Play's briefing on the importance of the natural environment for play at;

http://www.londonplay.org.uk/document.php?document_id=584