The staggered school return times you mention could be one factor (as could better weather resulting in outdoor socialising instead of indoor). The effect when schools return (~2 weeks from now in Scotland) might be muted however as hundreds of thousands more vaccinations will have been done in the parent-age population. In Scotland, for example, over 90% of adults have received the first dose, and 72% the second (implying that ~18% are in the waiting period for the 2nd). Perhaps we should expect to see a spike in cases in children, but not so much among their parents.