In reply to alanthomas:
Loads to choose from, but how about:
Arthur's Field at Portscatho
https://www.coolcamping.co.uk/campsites/uk/england/south-west-england/cornw...
Coast path and pub both just minutes away. Great for kids. Stayed there last year.
Henry's campsite near the Lizard, not far from Kynance Cove
http://www.henryscampsite.co.uk/
Haven't ever stayed there, but friends with children have and say it is lovely
Blue Hills camp site, at Trevallas, just along from Trevaunance Cove (=St Agnes beach), where you have the Driftwood Spars
http://bluehillscamping.co.uk/
Haven't camped there for years, but go past it often.
Treyarnon YHA campsite
http://www.yha.org.uk/hostel/treyarnon
Never stayed there, but go there often. Right on the beach. Padstow not far way.