My frien dis anursery nurse, although stopped working as one. She actually took her own chil dout of nursery as they room was left unsupervised and full of children and Offsted (I think it's offsted) are currently investigating the nursery because it is not allowed for children to be left unsupervised and grounds to close the nursery.
Personally, I would be absolutely fuming. This a nursery setting, not a home one, where people are paid to make sure your children are safe. I am a hairdresser, and even the finest of childrens hair would be hard to cut off if it was in a full ponytail unless you had pretty sharp scissors. Yes, it's onyl hair and no harm was done, but what if the little girl had accidentally (or purposely, god forbid) stabbed someone in the eye with scissors, there could now be a blind child due to lack of supervision.
I would also wondr what else had happned at said bursery. The one I mentioned above had also had a hair cutting incident (unsupervise child able to get scissors) and a child found out on the street. If they are negligent in one area, I suspect it spills over into others aswell.