Even if there are children involved, there is no minimum income requirement unless the children have children of their own. Remember, a "child" up to the age of 22 is considered, for immigration purposes, to be a dependent unless they are married or in a common-law relationship. So if an unmarried, under 22 year old child of yours has a child, minimum income requirements kick in - I believe even if that "child" is not accompanying you to Canada.