We just did the Blue Lagoon this past monday, Dolphin Swim. My daughter really loved it. The people were very friendly. I went as an 'observer' and got to take pictures and watch the whole thing. She was in the water over an hour. There were 9 people in her group and all got to hold, dance, pet the dolphins, and then were pushed across the pond by one. The encounter groups were on platforms, about waist high in water, and they also got to pet, hug, dance with, etc., but didn't do the swim across the pond. It was perfect for the younger kids and would have been enough for me. We could have stayed and swam at the beach but my daughter was cold and wanted to get back to the ship.
The next day I was talking to a family with young kids (4 and 6) and they'd done the encounter at Atlantis. The mom told me they knelled in the water and the younger kids got to be pulled around the pond holding the dorsal fin. I think Atlantis is a lot more money?
I liked the boat ride to blue lagoon very much. About 30 minutes, and you get to see fancy houses, including Tiger Woods' and Michael Jordan's.
Nancy