I'm in Cumbria. All schools in this county have advised that children with a positive case in the household (so any household member, not just siblings) need to stay at home and isolate until day 5, take a test, and if negative, return to school.
I can see both sides to it. On the one hand, Covid is bad, we all know that. On the other hand, experts are moving more and more towards the view that we are all going to get it eventually, probably multiple times, and this just feels like delaying the inevitable.
Plus, if, for example, DH were to test positive, then DC could not go to school, but under "the rules" I could take them to the cinema, soft play, bowling, shopping, museums etc., or any other crowded space you can think of.