You will have to provide us with documents that show your financial resources for the past 12 months and prove you are financially able to sponsor members of the family class. You may solicit the help of a co-signer (must be your spouse or common-law partner). If you reside in Quebec, see also Sponsors living in Quebec.
This condition does not apply if you are sponsoring only
* your spouse, common-law or conjugal partner who has no dependent children, or
* your spouse, common-law or conjugal partner whose dependent children have no children of their own, or
* your dependent child who has no children of his or her own.
at http://www.cic.gc.ca/english/information/applications/guides/3900E2.asp
Seems to me that you fall under number 2, spouse whose dependent child has no dependent children of their own.