Go with what you feel you can handle. The ratios are set based on some proven somehow formula of what a person can manage of course the needs of each child is different making some more work than others as well as some ages more work than others.

I am mom to 4 - started care when my second was 4 months old and other two were born into the daycare and have always tried to stay full with 5 additional children which is the law in Ontario. I have found that once you can manage 3-4 you can manage any number - the idea here being you are out of hands and have to determine other methods such as using a stroller longer or expecting children to come when called or learn patience of more than 20 seconds and with your own patience they will learn to function as a group. Never had an assistant and the only relief I got was that my kids eventually started school and were gone part of the day.

That is not to say that everyone feels comfortable with such a large group and the caregiver being happy is more important. Also knowing that you might be losing a child is a good reason to add another one to the group just in case. Then when it does happen you can decide at that point if you want to replace or go back to less children in the group. One thing I did find was that keeping the age range as narrow as possible led to the easiest days as in having 5 babies/todlers was easier than 2 babies, 2preschoolers and an afterschooler as I was pulled in too many directions. Starting all young they just grew up together and for a period of time we never did a craft or played dressup until the group evolved into that kind of play.