I do not personally do it. I mention to parents if it becomes an issue.
Funny (or not so funny?) story about daycare providers trimming nails:
My SIL used to be a daycare provider and she did a weekly check of the kids and clipped their nails if they needed it. She never once mentioned it to the parents. One day; little Johnny came in with his mom, and as his mom was leaving she said "Oh, by the way. I noticed little Johnny's nails are getting long. It must have been a while since you trimmed them. You mind taking care of that today, please?"
Let's just say that mom got an earful about taking care of her own son's hygiene from that moment on!!