When I began teaching (in 1972) it was impressed upon me that I was 'in loco parentis' until the pupils returned home to the care of their parents. I'm not sure what has changed. It did mean that occasionally I would have to stay at school until a parent arrived, or else walk/drive the child home. Things seem to have changed.
I've no time for the way some of these teachers seem to be over-using their powers, but there may well be more to it than meets the eye. In my last school (very large comp. in Bradford) you were expected, if on duty, to stroll outside the grounds and shepherd kids back - unless they were 'home lunchers'. This was not only to protect them and save possible incidents with pupils from neighbouring schools, but also because somewhere in the local shops someone was selling them 'Whizz' (an amphet.) which caused immense problems in the afternoons.
So, I'm a bit confused about this. I'll ask about the legal situation next time I'm in school (Mon. a.m.).