Stomach muscles after pregnancy

I am quite small and seven years ago I gave birth to twins. I am 5ft 2' and weigh about 7 3/4 stone.
Since that time I have had a large excess of fat around my stomach (the rest of my body is fairly 'fat free'). I have also noticed that there is still a gap in the middle of my stomach between the two sides of stomach muscles, which I can easily place my fingers in between! I was wondering if this is normal or if it could have a detrimental effect if I did stomach toning exercices to try and reduce the fat?

Duplicate question
http://www.funadvice.com/q/stomach_muscles_after_pregnancy_8087