So I checked and yes this information is also on the CDC website. Please Please I'm begging you keep your not toilet trained children and their fecal matter out of the pool.
CDC - Vessel Sanitation Program - Frequently Asked Questions
Why are children who are not toilet trained forbidden from swimming in pools on cruise ships?
Children who wear any type of swimming diaper or who are diaper-aged are not allowed to swim because fecal matter may contaminate the water. This can expose other swimmers to fecal matter that is potentially infectious.