This is a link from the chief nurse and interim chief medical officer of NHS Test and Trace to parents and carers. It explains in what circumstances parents should (or should not) book a coronavirus test for their child.

https://www.gov.uk/government/publications/guidance-to-parents-and-guardians-when-you-should-book-a-coronavirus-test-for-your-child/letter-to-parents-and-guardians-when-you-should-book-a-coronavirus-test-for-your-child