Can you tell me how old a child has to be to legally babysit in Ontario

I do not think there is a set legal age.

It depends on the child's maturity.

From what I was told years ago (not sure if this is correct or not), but the age to babysit is 12 and the age to stay home alone is 10, both ages provided the child is mature enough to do so.

To stay home alone is 10 and to babysit is 12 years of age.