Dear [Name],
I would like to express my intention to return to work on [date]. My baby is now [number of] months old and I now have someone to care for my child while at the office.
I would like to thank the company for extending my maternity leave and for being supportive to a new mom like me. For a company that values its employees, I wish [insert company name] every success in all its future endeavors.
Best Regards,
Letterbarn
http://letterbarn.blogspot.com/