Preventing Pool Related Illnesses

Inform your pool professional in the event of contamination.
To minimize exposure to pathogens, swimmers should avoid getting water into their mouths and never swallow pool or spa water.
Showering before swimming can reduce the introduction of contaminants.
Wash kids before swimming, especially their hind parts.
Take the kids on potty breaks, whether they ask or not.
Toddlers should wear special "swim diapers" and even these are not foolproof.
Check diapers often. If you hear, "I have to go," this can mean the child is already "going."
Wash hands after changing a baby's diaper (and change kids in the bathroom not next to the pool).
Those with diarrhea or other gastroenteritis illnesses should not swim, especially children.
The education of parents of small children and other people with regard to good hygienic behavior at swimming pools is also important for improving health safety.
A well-maintained, properly operating pool filtration and re-circulation system is the first barrier in combating contaminants large enough to be filtered.
Rapid removal of filterable contaminants reduces the impact on the disinfection system thereby limiting the formation of chloramines, restricting the formation of disinfection by-products and optimizing sanitation effectiveness.
Here is a great article about swimming pool sanitation from Wikipedia.