My answer probably won't be popular with those that enjoy the resort's indoor water park, but in the interest of public awareness, here's what I found when I researched going there with a group of friends and our kids. (We were scheduled to be there right after it was closed down last year.)
I'm going to paraphrase but will provide links at the end for verifcation/further research.
The problem with indoor water parks is that 1) there are very high levels of chlorine used to kill the mulitude of germs that develop in the water from the hundreds of people who use them every day - including
lots of children. High chlorine levels can result in skin burns and rashes; and 2) there are germs, spores and other microbes that live in the air in such a humid environment which may also contribute to health problems.
But what is less well known is that when chlorine combines with organic material in the water,

a gas is released, which, when inhaled, can cause respiratory problems (such as coughing or wheezing), some of which can be very serious (such as an asthma attack or an injury to the lining of the inside of the lungs).
There is an actual medical condition called
Lifeguard Lung which refers to the physiological problems of lifeguards exposed to these toxins.
In comparison to Coco Key, the
Cape Codder's pool uses ultraviolet light instead of high chlorine levels to clean their pool water. (I give them a lot of credit for their forward thinking on that.) Sure, it's not quite as much fun to the kiddos as Coco Key is, but they will still have a good time, and there's a lot to do for the parents there, as well. From the Cape Codder website:
we have been thrilled with the success of our new High Intensity Ultra-Violet Light System. This revolutionary system (which is not required by state or local laws) uses ultra- violet light to destroy living organisms present in the liquid being treated.
What it really boils down to, to me: Chances are, kids will be fine at Coco Key. But is it something you want to take a chance with, especially with very little ones?
Happy and safe swimming, everyone!
What happened last year:
http://wbztv.com/local/Danvers.Indoor.Water.2.670301.html
Chlorinization:
http://www.straight.com/article/healthy-pools-mean-healthy-swimmers
Interesting tidbit from this article:
In Europe, ozonation has been the preferred method of sanitizing pools for 50 years. Ozone technology reduces the amount of organics in the water; chlorine must still be used, but in greatly reduced quantities. Chemicals are added to surge tanks and then put through a filtration system before the “drinking-water standard” water is funnelled into the pool.
Some of the largest pools in North America, including Disney’s water parks, use ozonation. In Vancouver, the YWCA and Century Plaza Spa pools are ozonated.
Air quality at indoor water parks:
http://www.eriecohealthohio.org/downloads/environmental/barryrice.pdf
Ultraviolet water technology:
http://www.watertechonline.com/article.asp?indexid=6634595