Hi, try Cofton Holidays, Starcross, nr Dawlish, South Devon. Beautiful site, great shower/loo facilities, beach a pretty walk through parks own woodland, also outdoor swimming pool if you don't fancy the walk. They have several overflow fields so you might be lucky!
If your a group you may find it hard getting in somwhere as most sites dont allow groups - try sunnyside or rosecliston in Newquay, they both allow groups but will probably be expensive !
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.