House Without A Key is a lovely, upscale restaurant overlooking Waikiki beach. At first glance, it looks too nice to bring kids along. Here's the secret - the staff is incredibly welcoming, there are reasonably priced ($5-$8.50) children's meals, and there's a big lawn adjacent to the seating area. While we dined, the kids quietly played duck-duck-goose with other kids, practiced their hula moves, and generally had a great time.
Having dinner here, and watching the sunset as Kanoe Miller danced hula is one of my fondest memories from our trip to Waikiki.