This is a touchy area. Since the incident just occurred, we would try life saving measures, even if we are pretty sure there is nothing that can be done. One, it gives the family closure (we hope) that everything was done to save the child. Two, just in case. People do survive from the "unsurvivable" injury. When I say life saving measures (in a case like this) I mean, bag the kid until you get it in the ambulance. CPR may be initiated, but it cannot be stopped until arrival to the hospital (unless orders are given from the recipient hospital ER physician) and care transferred to the hospital. Doctors are typically supportive of EMS initiating life saving measures because it's a kid.
If the injuries are consistent with death, then nothing will be done. Just because there are stab wounds and lots of blood does not mean someone is dead or will not survive. But I'm talking about partial decapitation, decapitation, or other more gruesome scenarios. If the kids were in the tub for hours and were showing signs of lividity, then we wouldn't do anything. I know it all sounds contradictory and doesn't make sense, but it because pretty complicated with children are involved.
Also, this case can't be compared to the Morgan case. She was showing obvious signs of death. Period.