@SerafinasGoose
Another person's emergency shouldn't have to become my emergency. However, my child is involved, so this makes it mine. Work, caring, other commitments will have to be dropped whilst I go and get them
This is exactly the point though isn't it. The OP has made her emergency into the parent's emergency and imo thats unreasonable of her especially considering* *that we're clearly not talking about the heart attack of an immediate relative - OP had time to post on mumsnet, didn't have to leave until the next day and has now said it concerns the children of a relative. So, sounds like childcare. But the point is she was already in a childcaring role, looking after the group of girls in her care!
Yes, parents should always think about contingency plans and know that they can get to their child if needed. And yes, the accusations of kidnapping are OTT. But the OP asked if she had done anything wrong, to which the answer is yes. She took responsibility for a group of children, the children's parents trusted her to look after them but she then decided to palm them off on someone else unknown to the children and parents so that she could go look after a relative's children instead, presumably because she cares more about relatives children than the ones she agreed to care for. Even if you argue that its the parents responsibility to make sure they can get to their child/drop work/drop other commitments etc, its still bloody inconvenient, could cost them money/time that they can't really afford, cause all sorts of problems and the point is that this isn't what was agreed. The OP agreed to take care of those girls for the week and return them safely home.
The way I see it, the only way she can be forgiven for going back on that promise would be life threatening injury, natural disaster in which they get separated or the sudden or impending death of a very close family member. It doesn't sound like any of these things apply. So yes, she has done something wrong and she is unreasonable in this situation.