Chronic non-specific diarrhea of infancy aka toddler's diarrhea
also see Diarrhea, Viral gastroenteritis

Pathogenesis

DDX:  important to work up ddx, since many of these are serious...

Treatment

Referral, if no response after 2 weeks, growth delay, or other GI/systemic complaints.

Keep in mind:

Normally, the intestines preferentially secrete potassium bicarbonate into the lumen and reabsorb sodium chloride. Because diarrheal stools are high in in potassium, increased stool output can lead to depletion of potassium stores.

References:
Baldassano RN, Liacouras CA. Chronic diarrhea: a practical approach
for the pediatrician. Pediatr Clin North Am. 1991;38:667-686
Davidson M, Wasserman R. The irritable colon of childhood (chronic
nonspecific diarrhea syndrome). J Pediatr. 1966;69:1027-1038
Kneepkens CM, Hoekstra JH. Chronic nonspecific diarrhea of childhood:
pathophysiology and management. Pediatr Clin North Am. 1996;43:375-390