My kids were ill from time to time, it happens, but I was always on the phone to the school the moment I thought that someone would be there. They never called me, I called them.
And if they were uppity with me, I would simply have said that my child was still ill, because, IMO they still are for a full day after a gastro. If they had asked if I had seen a doctor, I would say that if they got any worse, I'd be taking them to see the toubib and if not, then they should be in the following day and if not, I'd call again at the same time the following day.
And our GP did not appreciate having his waiting room clogged up with minor ailments.