A bit of background: My ex husband's new wife is extremely controlling, coercive and bullying towards him. The ex and I aren't the best of friends, but I do feel very sorry for him and still care about him as my kids' dad. Sounds pathetic, I know, but it is obviously an abusive relationship. He's a broken man.
Terrible situation, but one that he has chosen nonetheless, and whilst it has affected me financially (she insisted he override his consent order with the basic CMS amount) and has severely damaged my co-parenting relationship with their dad (she won't even let him speak to me), until now this wasn't particularly affecting my kids who, so far, she has been perfectly lovely to. It's something I'm keeping a very close eye on.
But the latest crazy thing they're doing IS affecting my kids, so I want to know if I have any power to stop it, legally....
He's moved 45 mins away from their school and picks them up every Wednesday and every other Friday. For the last 3 pickups he's driven them round the corner from school and parked up in a Co-op carpark where he's made them take a lateral flow test for Covid. They are 7 and 9 and the government aren't currently recommending testing on primary age kids, but this is obviously a condition of them being allowed back to his home.
I know this isn't harming them physically, but I worry about the psychological impact: My kids can go to cricket, ballet, brownies and school without being tested but they can't go to their dad and step mum's (neither of whom are shielding or vulnerable) without proving they haven't got Covid. Also: In a car-park??!!
....it's like they're dirty little street rats or something 
My opinion is that it's physically uncomfortable for the kids, unpleasant and sends out a harmful message about their status in their dad's household. I've told him it's against my wishes and against government advice and have asked him to stop, but he's carrying on doing it 
Is there anything I can do??? Even if this particular issue isn't the end of the world, I kinda want to flex a bit of muscle here to show them they're answerable to me when it comes to the kids and that whilst their own life is utterly crazy they can't just do any old irrational thing with my kids.