Corfu has good beaches and ok ruins...
Minorca has good beaches, outstanding roman mosaics, a gin factory 

etc
If going for cheaper option, the Eurocamp at Domaine de Drancourt, easy drive from Calais, pools, beach pretty close, short drive, the castle where William the Conqueror set off from and Joan of Arc holed up in, outstanding bird sanctuary the other side of the estuary, ditto fantastic restaurants, mini train round the estuary, they do day trips to Paris where you get up at sparrowfart but hey ..ok, so northern France so can’t be 100% sure of weather but one of our best holidays. Kids safe on site, go karting, playing badminton around, buying themselves pizzas at the shop, dragged them off to eat nice food ( not worth wasting ace food on them), BBQs by site, good supermarket close by, beach, donkeys in beach,, ( it was 10 years ago or so). Most relaxed holiday ever other than Langkawi in Malaysia, another brilliant holiday but long haul.