Keeping Weeds Out of Mulched Beds?

I recently weeded and mulched all the trees and two large flower beds at our school where we have an outdoor learning space. The town's grounds keeping crew cut the grass and blew all the grass clippings over the mulch. (We met prior and they said they would be careful, but someone did not get the message.) All the mulched areas have a thin layer of grass now. Is there anything I can do immediately to prevent grass and weeds in the near future? I'm devastated.

By Katie