I think they're being utterly stupid. Unless you've all been isolating, completely, for the 12 weeks you cannot say you or your family are not asymptomatic with Covid 19.
I go out each week to my local supermarket. I've careful but we have to eat. I have no idea if I pick up something from the shelf that has been handled by a person with Covid. I bring that item back into my house.
People have had to work during this - whether that's NHS, delivery people, supermarket staff. I have had to go to my post office each week as I have a small business that's keeping the wolf from the door at the moment and have to send out orders. It's always busy. There's sanitiser at the door but how do I know if everyone has used it? The woman who runs our post office sanitises after each customer but she can't wipe down every counter that a person with Covid has leaned against.
So the kids may have been home for 12 weeks but every time they or their family has been out they, potentially, bring the virus back home. Therefore they are not 'safe' or 'germ free' and, unless these women are consenting to their kids having the nasal/throat test done, they cannot prove that.
So social distancing has to stay in place and they'd be better off teaching their kids why, how it works and treat it like a big game that they and their friends are all part of.
Testing or social distancing - their choice.