Have you considered Bedruthan Steps or Newport Bay in Cornwall? No narrow streets, great beaches with tons of space, and lots of great activities for adults too. Great cafes and restaurants to chill in with a well earned latte/glass of wine, snack/full meal, with fab views. (Surf schools for the more adventurous). Don't be too disheartened with your last holiday experience, but remember that it may not all be entirely relaxing with young children.