I would be sending out an ammendment to the contract that says as of whatever date the daycare ratio will be subject to what is acceptable by the Ontario Day Nurseries Act of one caregiver to five daycare children not including her own children and even quote the passage directly if you wanted to. Let's them all know that you have every right to do this. Then include a form for them to sign, date and return that says they agree. And if not that you will take that as their two week/4 week notice - I would be giving them plenty of time since it is you changing what they thought they had signed on for but it is your business and if they leave their choice.