Has anyone's DC's school provided proper informed consent forms for the LFTs and explained what happens to the test results - how they are processed, how the results are stored and the legal basis for processing this data under the data protection law/GDPR?
A medical test can only take place after informed consent has been given (with information in writing), after you have had the chance to ask questions and these questions have been satisfactorily answered.
Medical test results will be subject to data protection law. Schools must explain the legal basis for processing the data. They must state who has access to this data and who processes it, the fact that unauthorised people cannot access this data.
The legal/ethical/professional medical issues surrounding these LFTs have not been handled correctly.