fecal occult blood test
is done to determine the presence of microscopic or invisible blood in the stool, or feces. Fecal occult blood can be a sign of a problem in your digestive system, such as a growth, or polyp, or cancer in the colon
. If microscopic blood is detected, it is important for your doctor to determine the source of bleeding to properly diagnose and treat the problem.
So you don't have to wait any bleeding that visible in your childern's stool to take the sample, just take the sample anytime your child poop, good luck :)