I love Cornwall.
We always head down to the Lands End Peninsula as we tend to do a wrking holiday at The Minack Theatre with my theatre group.
If you head that way, I really recommend seeing the Minack Theatre ( and see a show there if there are tickets available - they do childrens shows on certain afternoons in holiday season).
Porthcurno beach, next to the theatre, is beautiful and often has seals, dolphins and basking sharks swimming nearby.
Sennan Cove is also a lovely beach.
Goonhilly satellite station is close by on the Lizard Point, and has a good hands on tech museum.
There is also a Seal Sanctuary, and if theme parks are your thing, then a trip to Flambards is a must.