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Sheringham Splash is ok, has a 'beach', good for mixed ages - don't know about Hunstanton. Norfolk not great generally for swimming pools. The pool at Kelling Heath fitness club is great but expensive unless you're staying there. Alternatively Pinewood Park Leisure centre at Upper Sheringham. Good sea swimming at Wells, Sheringham, Cromer, Holkham but check that tide is in otherwise it's a long walk!