I think zero tolerance will be difficult unless all staff in the school are the same, and are backed up by effective SLT.
For reasons of age and underlying conditions, i am very scrupulous about following Covid guidance in school, whereas many of my colleagues (younger and / or no underlying conditions) are much less so. SLT are a mixture of scrupulous and lacksadaisical, led by anything-for-an-easy-life-and-to-be-liked-by-parents.
I entirely anticipate sending a coughing child to be sent home, to have them returned by leadership with a 'oh, it's nothing, and we don't want to bother mum / dad because they're at work so just keep them to the end of the day' [have had it before with vomiters], and to be the only person who makes a fuss....