In UK, a child under 16 whose parents are of a particular religion (for example, Jehovah's Witnesses) is made a Ward of Court if they need, say, a blood transfusion or an operation needing blood and the parents object. The Court overrules the parents, who have no say. This applies to any life-saving procedure, and any harmful procedure (Female Genital Mutilation for example) The Court can forbid or enforce medical procedures to protect the child. This Law can be invoked even in the middle of the night if an emergency should arise. A Judge will be roused from sleep to exercise control of the situation.

You've raised an interesting point Mrrzy, as 'allowing a child to die' could be seen as rather different, but still, the child remains at the centre of the Court's decision, not the parents. If a Judge deems the continuation of life to be unethical, s/he is the one who orders that care be changed to 'palliative only', and this must be obeyed.