Delivering food and water to patients using a tube is called enteral nutrition. In the case of patients that have no higher brain function, but are still capable of living without life support, enteral feeding is a routine procedure.
There are many cases where a person is brain dead to a point where they will never wake up, yet have enough brain tissue intact to breathe on their own. In those cases, the only way for them to be allowed to die, is to withdraw enteral support. This is done all the time here in the states. I have never heard of it being done in a pediatric case, but then again, I do not work around terminally ill children, thank goodness.
Look up Terry Schiavo. This is exactly what happened to her.