Nassau shore excursion ?

[chance]

We are sailing on the Wonder 10/27/02. Trying to decide btween the Atlantis beach day and the Blue Lagoon Day. We have 2 small children, 4 and 17 months. I leaning toward the Blue Lagoon but have some questions:

1. Will it make the next day at Castaway Cay boring doing 2 beach days in a row?
2. Is there shade at Blue Lagoon, i.e. umbrellas?
3. I know you depart at 9:15am but what time do you get back?

Thanks so much