How old are the kids? It is highly unlikely the under 2's will leave because of the increase (there aren't many places for them to go to).

I would possibly consider increasing the under 2 spots for November 1st and waiting until January 1st for the over 2 spots. That gives you a bit more income but gives the families with older kids a bit more time to budget. Assuming you feel the families need more time to budget. If you suspect your cliental can pay that much more without much notice then go for it.

Unfortunately Bill 10 has created this mess and there really is little that you and the families can do about it. You need to survive and the families need care. But, some families will really struggle with a big fee increase.

In your letter let the parents know it is due to bill 10, that changes the ages and numbers of children you are hit financially and you cannot continue care without increasing the fees.

Best of luck!