HI: Its great a great question. A normal stool should float be approx 5-6 inches and 1 1/2 inches in diameter. It should move easily and quickly with little straining and odor.
Stools float for 3 reasons: 1: as you mentioned undigested fat in feces, not good. 2: gas bubbles in the stool, not good. 3; high fibre diet with proper balance of intestinal bacteria, very good.
The intestinal bacteria acts on the chyme as it enters the large intestine (bowel); as it breaks down the food particles the bacteria helps to manufacture many of the b vits and other nutrients used by the body. These bacteria work on the soluable and insoluable fibre present in the chyme it is this action that creates the proper fibre balance- floating stool.If the proper fibres are lacking , the bacterial balance off ;and the diet poor; the resultant effect is a sinking one.
So when any type of cleansing is done especially using substances that affect the intestinal bacteria replenishing is the essential next step after the cleanse.
Your son's stool is normal for his age as the bacterial balance changes with age and diet usually around age 5-7 depending on DIET the stools will have more predominant lacto A and float.
Most people want to cleanse cleanse cleanse but forget to replace and rebuild after each cleansing period. Hope this brief explanation of digestive function helps.

It is great you ask first; too many gobble down supplements and cleansing products without question?Harmful? Helpful?

ND

A healthy stool should sink, that replier is wrong.