Yes a child was injured. That is not in dispute, in spite of people over the internet arguing.
There are school procedures that should have been followed and were not, both by the teacher and by the parent.
However, the parent COULD have gone to the headteacher and followed the school complaints procedure and had this investigated, the normal thing to do.
Instead they called the Sun newspaper and the police, causing a person to lose their job and to spend A YEAR worrying if they may lose their career.
All this at the time when the profession is losing good people hand over fist, so well done that parent.
The same people and the Sun newspaper will be complaining when their school kids have a succession of supply teachers rather than a permanent one.