E.D.
Hi N.! I actually teach a course in Women's Psychology and most of the research suggests that the factors that matter most in children's adjustment to mom's working is the quality of childcare (which it sounds like you have arranged) and mom's own happiness and satisfaction (which it sounds like your job can bring). Chances are if you feel good and enjoy your work outside the home, your children will benefit...this is especially beneficial for young girls to have mom's as role models in the workplace.
I also have read and recommend a great book that addresses these issues called "The Birth of a Mother" by Daniel N. Stern & Nadia Bruschweiler-Stern