If you don't send your kids to school I can't see a legal defence against fines. Fine for middle class parents who may just take a punt on keeping kids at home, knowing they can pay if needs be. But it's dreadful for poorer communities, already disproportionately hit by Covid.
The solution seems to me to be for teaching unions to take and publish legal advice on whether their members are obliged to risk death or can choose to stay at home. Pretty clear to me what the answer is likely to be. No teachers means Government will have to change course.