I would not close.

I normally assess if there a safety of health/hygiene risk to the children. Since you have ability to flush toilet even if it with bucket of pool water and wash hands, then I don't see being an issue.

If there had been a risk to children, I would close to all and lose that day pay. If there no risk, I would inform parent and then up to them if they chose keep child home but they will pay because I open and willing and able to work.

Just a side question - I think you in Nova Scotia - are you allowed pools with your daycare insurance? I thought pools and trampoline mean decline cover across all province. Can I ask who you insure with?