Q.I Cut Off The Tops Of The Celery Thinking It Was Parsley. Did I Ruin It’s Growth?
As Mom I was asked to take the first cutting when the kids left for vacation. Did I ruin the. Celery growth?

Certified GKH Gardening Expert
It depends on how mature they were. If they were really young, then it is possible that they are going to die. If they were well established, then there is a chance that they will come back.
Here is an article that will help you with the care of celery:
https://www.gardeningknowhow.com/edible/vegetables/celery/tips-on-how-to-grow-celery.htm