When you get home, pop in a good chic flick and just cry!!
When my oldest went to K, I stood in the house and cried. Then that afternoon he asked why I had been standing at the window instead of saying goodbye at the bus stop? It was then that I knew he was okay.
One thing that will help with the younger one on monday is if you take her stuff: extra clothes, diapers, wipes, etc. to the center tomorrow or friday. That way when drop off time comes on Monday, it will be less chaotic and less stressful. You baby girl will take a lot of her cues from you. Don't be too over excited, she'll think your setting her up for something. Just be yourself. Try to be calm, and it will work out. Try not to cry until after you've turned the corner of the building.
I had a bad morning one time. Went to the car and cried. When I was ready to leave, I looked up and my son and his friends were all standing at the window staring at me. Apparently I was good tv! Ooops!
Hugs
M.