I've just read the regs (I'm familiar with the Civil Contingencies Act and regs made under it) and as expected, there's provision (section 7.6)for people potentially being quarantined to make representations, ie argue for an exception to be made, usually on the grounds of someone's welfare.
So I'd advise OP to ask what the procedure would be to ensure suitable care for her children if her hospital got locked down. I suspect it would involve some phone calls to PHE, a hastily-written licence to permit OP to be transported in the back of a black cab to her home and then requiring her to stay there and family to stay away from crowds, and various conditions on disinfection, but couldn't say for sure.
There's also the right to appeal the quarantine decision, to the magistrates Court, but that would take longer.
My non-professional advice to OP is to ensure managers in her hospital are aware she is a carer, find out how they would operate exemptions to quarantine, and also prepare her kids and childcare staff for a possibility of some hours before they could get reunited.
PHE epidemiologists and contingency Planners aren't daft and are well aware carers exist.