sowhatnow - it's not clear what the motivation is. My understanding from talking to someone who has been very close to the situation is that, to best of their knowledge, the child was not subject to a court order nor was blood a factor.
The parents' action is a a surprise to those in the congregation and their intentions are not known. The reports on the BBC reflect this. The police are keeping an open mind and there is nothing to suggest a direct link between the parents' being Witnesses and their actions.
The big concern now is that the child has a feeding system that requires batteries. They believe the batteries will have run out in the last hour. Without proper feeding his condition will deteriorate quickly. It may be that the parents can recharge the battery or have spares but this is not known.