There are three man-made but truly beautiful lagoons: one shared by JW Marriott and Disney Aulani hotels, one in front of Beach Villas at Ko Olina condos, and one in front of Marriott Beach Club. The shared one is much more crowded, but has rentals of kayaks, paddle boards, etc. All are accessible from small public parking lots as well, so you can bring your own food and drink for beach picnics. The man-made deposits of rock reefs allow fish and turtles in but keep waves away, so this is perfect for smaller children. It does not allow for any surfing or boogie-boarding. Walk north past the JW Marriott to an amazing little cove that attracts big sea turtles, even in thigh-deep water. Teenagers might find these too tame. Just south of the Marriott Beach Club there is a harbor with snorkel trip boats.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.