MYT--If you are still on maternity leave and a member of a union, contact them--if you are not, join one!!
I have been job share with a national airline for over 12 years, which i had to fight for, after having my 3rd child.
However,there are laws in place now allowing parents the right (all be it limited) to part time work after having a baby--remember the BA pilot Jessica ?
If you are not in a union contact your local CA, but be prepared for a fight with your employer!!!
Best of luck.