Nothing new to add.... but what all the others have said is exactly right, in my opinion.
It is hard to listen to a child cry for any length of time, but allowing them to learn to get to sleep, stay asleep and go back to sleep if they wake up too soon is the BEST gift you can give them.
I would absolutely have a chat with mom or dad, and let them know that a child in group care needs to learn to self soothe, and that in the long run, it will benefit everyone.