Laurie71, I want you to stop for a minute. Go open a window and sit down next to it. Now, Take a deep breath into your lungs, then hold it for the slow count of 3. Then, push it out through your mouth until it is all out. Not fast, but do that several times. It will help calm you.
If you need to, put your head between your legs and just hang that way for a second or two. Then, sit up and shake your arms out. Wiggle them about and then, just relax them.
You are going through the first phase of your PTSD, and the first of anything is always the worse. You know? The trick is to learn different forms of coping. Have you found a good trauma therapist yet? If not, I recommend you start searching for one. And don't go to just anyone. Make sure they know about trauma and how to cope when one has it. If you need more tips, let me know I have a few pages of them in my diary/journal I can share with you.
I do hope you enjoy the children tomorrow and don't worry about yourself during the time you are with them. Just concentrate on them, and all will be well.
Good luck. See you around the forum,
Safenow