"Nanny, we talked about cleaning up the playroom before you leave, and I realize it's totally unfair to you to ask you to stay late to do this since you get back from pickup at 5pm. So can you please clean it up before you leave? Its OK if Larla watches Paw Patrol while you finish that job."
If it doesn't improve: "Nanny, the playroom still isn't clean. Is there a problem? How can we fix this?"
If it still doesn't improve: find a new nanny.