I am support staff in a secondary school, and I have worked at school throughout the pandemic (and currently self isolating at home!!), I can say that some families are anti-masks and anti-tests (and anti-vaccine) and will find every little excuse in the book to make sure their child doesn't wear a mask or doesn't do the test.
For example, my son has acne so he can't wear a mask. They will argue with the school on and on and on about it. The child will follow their parent's example and argue on and on about it. THe tests is uncomfortable and makes my child gag. THerefore he won't do the test. We hear it all the time.
It's amazing that people are so naive and think that kids who don't wear masks all have a good reason not to wear one. It's just like adults. England is full of little Laurence Fox, pretending to have an illness in order to get out of obeying the rules.