There's a reason that schools have been closed in literally every country that has serious numbers of this disease. China, Japan, Singapore, South Korea, Italy, Iran. Germany and France are closing schools in hard hit areas too.
It will happen at some point, whether a whole country closure or localised, it's a question of how effective it will be - this is linked to when it happens.
The Chief Medical Officer in this country has said school closures may happen
www.bmj.com/content/368/bmj.m806
It's not like people are plucking this idea out of thin air. Desperate times call for desperate measures. They must have found solutions for the healthcare workers in all the many, many other countries which have had school closures.
It's not closing schools for no reason - if schools are closed it is likely there will be fewer healthcare workers off sick as a result of the decrease in transmission. It's not close schools, massive inconvenience with no benefit to the NHS and it's staff - the reason this is being considered is to help the NHS and it's staff (as well as save lives - again related to the strain on the NHS).