Stuart,
Perranporth in Cornwall was fun with my kids, Deauville (for Honfleur) might be a bit of a long taxi trip.
Stornaway, Oban (if still available) are great for sight seeing. Edinburgh is pretty easy. Skeegness is fun but might be a bit short and grassy for you! Guernsey was great, never done Jersey or Alderney.
What I tend to do is go and check places out with friends before taking the family, only problem is that I tend to forget about taking the family!