Now i know its not the most obvious place - which is part of its charm but we recently stayed at Littlehampton, they call it 'Sussex on the sea' and the boys loved it, wide variety of days out and glorious beaches. Fun park on the seafront was good value and tired them out...always a bonus
we found it through the link below, theres a video on the site which shows different stuff, neat idea
Family Holidays South England | Family Friendly Holidays UK | Family Day in South East