White feces is usually related to bilirubin metabolism disorder. Bilirubin is a part of the bile. In the intestines it is transformed into sterkobilin which gives the feces it characteristic brown color. Without it the feces is white.

Since the bilirubin is also needed for fat absorption, the feces might be oily. You might want to take your grandson to a pediatrician and check his gastrointestinal tract including the bile production and excretion.