Seems your son has ingested something nonedible which has infected him and also has come out of his gut now. If the diarrhea
continues, please do not wait and see a pediatrician
as you cannot afford to let the child develop dehydration
due to frequent stools and plus the doctor will advice antibiotics to be tried first hand (empirical ones) just keep the diapers in clean polythese bags, say ziploc bag or something, and carry to the laboratory. In the lab they will take the sample to check the stool. This is essential for deciding further steps in the treatment if the empirically used antibiotics do not work for your son. Also the doctor will treat your son with antidiarrheal if necessary. Meanwhile ample of fluid are must. Avoid milk for time being. Hope this helps. get back for further query.