At the head of Loch Brittle is a big beach. There is sand here at all states of the tide, and plenty of space for playing, kite flying and the like. The sand is not white, but that apart it is a beautiful spot. An added advantage here is the nearby campsite shop for ice lollies and cold drinks. (Or hot drinks and survival blankets, if you're less lucky)
There is parking for cars right by the beach. Go to the end of the road just before the entrance to the camp site, at NG409206.
For strong swimmers only:
There is much fun to be had by heading out from the beach, following the bottom of the low cliffs on the left hand side. Here you will find the burns that drain from the Cuillin forming great waterfalls that drop vertically into the sea. The best one is the 'Demon Shower', where the Allt na Buaile Duibhe arrives in some considerable style. After a sunny afternoon, the shower will be pleasantly warm, and very powerful. Always a better place to wash than in than the campsite toilets!