I have found the opposite- actually most of the children at my children's schools are very passive and do what the teachers/their parents tell them. Lots wanted to strike but their parent told them not to- so they aren't! I was initially skeptical but my children have convinced me that taking part in direct action on climate change is important. We've also had lots of conversations this week about what we can personally do (like turn off lights, use car less, we eat veggie mostly) so it's been productive.
I am worried by the passivity of the UK population (or perhaps just the English). Young people didn't vote for Brexit, and they are getting it anyway. I don't think it matters whether this one strike changes everything- it won't, but by continuing to push climate change up the agenda, and over-consumption (which is a huge problem even without climate change), politicians do listen. Direct Action is powerful.
I'm allowing my children (age 13 and 15) to go and I haven't sent them to school so there is no issue of the school being responsible for them/safety issues of leaving the premises. I agree this would put the teachers in a difficult situation, so they can side-step it. Both know they may get a detention/some school sanction for attending. I'm proud of them.