update:
He is still in the hospital.
He was moderate to severe dehydrated when admitted (moderate, but on the edge of severe).
He is getting some energy back. He FINALLY ate "club crackers" tonight, but still isn't drinking much of anything. His diarrea is HORRIBLE and his rear is RAW. So, he is still there tonight, until be begins eating and drinking SOMETHING.
They are pretty sure it is Rotavirus (test results in tomorrow). It is a rather harsh case of it, if it's correct. There were several elements that caused marked concerns for the medical folks (which my mother-in-law understood).
I'll know more tomorrow.

Thanks for the prayers and notes of concern.

Thank you all,