Read this before starting any ab workout or core routine!!
Your muscles may be separated because of the c-section. It depends on how long ago you had this done. Instead of me rambling about it (I've never had a child yet)... I found this awesome post by one of my fitness collegues, Helen Byrne:
========
I can tell you that a separation of two finger widths is normal at six weeks postpartum. And that the shape of your belly is NOT related to abdominal separation. You've got two separate issues here. Getting back to pre-pregnancy looks and possibly muscle separation.
To flatten the abs after pregnancy, you need to start with the most interior layer of the abdominal wall, the transverse abdominus. This is your internal ''girdle'' muscle. By building strength in this muscle first the abdominal wall will remain flat upon exertion. This is a very important concept of postpartum conditioning.
In fitness, what you pratice is what you get. And if you do crunches without the underlying internal support your belly will definately bulge. Bulging of the abdominal wall actually increases abdominal separation. (I've also found that most women do not perform the abdominal separation test correctly.)
I do not recommend oblique crunches. Oblique work can place shear forces across the abdominal wall, worsening abdominal separation, especially if the transverse abdominus is not strong enough. Generally, many types of traditional crunches are contraindicated for those with abdominal separation.
It is also important to note that abdominal separation is only a problem in the first months after pregnancy. Yes, the rectus abdominus does not go back to it's original position, but once your connective tissues have tightned up, (anywhere from three to six months post-pregnancy) you won't have a hole there anymore, and you will not be at risk for herniation. It is a myth that you can't have flat, strong abs after abdominal separation.
===== END HELEN's Response ====
So you see it totally depends on your situation. You could actually injure yourself big time by doing a traditional core routine or ab work. Hope this helps you a bit.