[Gayle]

So, I've just been doing some googling to find out what the legal position is and one interesting thing is that the children were breaking the law (well, actually their parents were breaking the law and could be prosecuted for not having them at school on time).

Theoretically then, the shopkeeper, instead of serving them butties should have been phoning the police.

The teacher who was trying to get them to school was ensuring that they weren't breaking the law.

I also found this statement
Local authorities (LAs) are responsible, by law, for making sure parents fulfil their responsibility of ensuring that their child receives an education either by regular attendance at school, or otherwise. Most LAs employ education welfare officers, (also called education social workers) to monitor school attendance and to help parents meet their responsibilities.

To me, that sounds like the teacher was perfectly within their rights to tell the pupils to go into school.