Please note that the guidance states:
The Government has asked parents to keep their children at home, wherever possible, and asked schools to remain open for those children that absolutely need to attend…every child who can be cared for safely at home, should be. If it is at all possible that a child can be at home, then they should be.
Therefore, if a parent is in the key worker group but can arrange safe childcare other than school they should do this. This is to ensure that we protect those workers who are in critical roles from infection as far as possible.