i think it would be better for you to call the embassy regarding your case as soon as possible...
And also have a look on this, hope it will help.
If you change your mind about sponsoring, you must write a letter to the Case Processing Centre of Citizenship and Immigration Canada in Mississauga, Ontario, before the permanent resident visas are issued. Once permanent resident visas are issued, however, the promise that you and, if applicable, your co-signer made to support your family is valid for the term in the application.
The application is an unconditional promise of support. For example, if your relative is granted Canadian citizenship, if your relationship breaks down or if your relative moves to another province, the application will not be cancelled. Even if your financial situation changes and you can no longer afford to support a relative, the application remains in effect. You must support the relative financially for the full term of the agreement. http://www.cic.gc.ca/english/information/faq/immigrate/sponsor/relatives-faq04.asp
So if i were you, you have to act as early as now because once your husband is in Canada, you as his sponsor is oblige to support him in 3years. i don't think your child's application will get affected once you cancel the sponsorship of your husband.
God bless and hope everything will be fine .
