Is there anything I can give him????

We had carvel yesterday after the beach and DS was in the bathroom 3 or 4 times and I heard him going and it was definatley loose (sorry for the TMI!). I thought he was better but DH was home with him this morning and DS told him he had a belly ache and went to lay down and took a nap! Very unlike him.

He has no other symptoms. Just the belly ache and loose stools. We're keeping him hydrated but is there anything else?