Hi Glogirl68,
This is coming many months later but I saw this question and thought I would answer. Here are the following fees:
Sponsor a dependent child
Sponsor only a dependent child ($75 sponsorship fee and $75 processing fee) or include one on an application with your spouse or partner ($150)
150(per child)
If you had included the child as an unaccompanied dependent on the form, it should not be a long process.