It's totally inappropriate to call CPS because they were reluctant to take the kid to the hospital for vomiting/diarrhea.
My son ran a couple really high fevers when he was younger (like 104-105) and we rushed him to the hospital. Each time was stressful and non-productive. The doctors subjected him to a bunch of standard tests, concluded he had "some sort of virus/bug" and sent us home to continue our Motrin/Tylenol regimen. Eventually we realized that he just ran really high fevers, and since then we don't react that way unless it persists for a long time or is accompanied by other unusual symptoms.
In short, even if they aren't going to win the Parents of the Year award, they know their kids better than you and it's none of your business.