Sit ups and Crunches -are NOT the answer!!
What if I told you not to do sit-ups or crunches? My sister in law had a c-section a few years ago, and her Dr. told her after six weeks she could start doing crunches. I cringed because I know that crunches or any exercise in which you raise your shoulders off the ground from a backlying position, will make it impossible to hold in your transverse abdominal muscles and give you a bulge out, right at the belly button. The problem is, there is a weak point in the connective tissue at the belly button and crunches can cause a diastasis, or separation of the rectus abdominal muscles. If you already have a separation from having a baby (most all women's recti muscles become separated as a result of the growing uterus when they are pregnant), than crunches will make it worse!!
So, what is the answer? The Tupler Technique®, which teaches you to pull the belly button in towards the spine in everything you do as well as specific transverse muscle exercises to start with to strengthen the transverse and bring the two halves of the rectus abdominals together, so the separated connective tissue can heal.
You must also avoid certain movements like jack-knifing in/out of bed and certain exercises which cause the belly to bulge out at the middle, making your separation worse.