It’s inevitable now. I think there are two reasons:
Children and school staff are not protected. We are the only country apart from the Netherlands (who have closed schools) to run our schools like it. No safety measures, no masks for the majority of the time. Also our schools are overcrowded.
Secondly, viruses mutate. It is quite possible, that with everyone happy to let it run through schools and turning a blind eye. It has mutated to attach to the receptors of children more easily.
It’s probably a mixture of both. They need to find out because the continent is rightly scared of importing a version which is more prevalent in children.