A second vote for Kailua Beach. Gorgeous, easy to get to over on the beautiful east side. There is wave action, but it still feels very gentle. We spent a couple of hours bobbing in the waves floating on our boogie boards (bought cheap ones at ABC store and then passed them on on our last day). Our local friends went to the more northern end of Kailua Beach (they referred to it as Kalama Beach Park) for boogie boarding one afternoon -still very gentle but slightly better for boogie boarding than Kailua.