I had a similar situation with my ONLY daughter Caroline. She goes 5x a week, but only half days. The first week was horrible, and she's not always keen on mom leaving now, but she deals. THis is what I did.
Every morning, we'd get daddy ready for work, then walk him out. Daddy goes to work, Caroline goes to work, and mom is going to start going to work, now that Caroline is going to school. (I'm not really going to work, well house work, and stuff like that, the usual)
Then if she was a big girl at school with no crying, I'd give her something on the way home to munch on. (I always had an after school snack, now I"m just calling it a surprise for being a big girl). Ofcourse on the way home, we'd take time to discuss what she did, and would always make a big deal out it.
That seemed to work. Hope this helps.