The six-pack muscles, or "Rectus Abdominus" stretch from the ribs to the pubic bones. They are held together by ligaments, which become more flexible during pregnancy to allow for the belly to expand, separating the six-pack muscles.
Normally, post-birth, the muscles return together, though they may feel tired and stretched. It is vital to avoid sitting suddenly from a resting position or heavy lifting.
|Divarication of the recti: image from Miracle Physiotherapy|
A physio can assist in diagnosing divarication of the abdominal muscles (may require an ultrasound) and teach pelvic floor exercises that strengthen the deep abdominal muscles AND the six-pack muscles. According to LIVESTRONG,
You should wait three days after your labor to perform the check for diastasis recti. If you had a C-section, you should wait six weeks, or until your incision has healed.
It is recommended that if you have divarication of the recti, avoid sit-ups or leg-lowering exercises. Corrective exercises, as mentioned before, require engaging, strengthening and gaining control of the pelvic floor. If it has been over a year since you gave birth and the divarication still exists, surgery is an option.
I am not an expert and would not like to recommend any exercises as every woman has different needs. Mishfit is a Melbourne-based Pelvic Floor Training business. You can take up a free trial session and read more at Mishfit. You can take your children along to sessions!