Really it's sad that people worry about being nosy in other peoples business. You don't even know what she did with the kiddo previously. It doesn't mean she is a bad person. People are allowed to have breaks. Maybe she had an emergency. Stop assuming that you need to go report everything. How would you like it if your boss had a camera on you all day. Why don't you look at how you would feel reported on something silly or go up to the Nanny and tell them who you are at least and explain that it bothered you.
Really it's sad that people worry about being nosy in other peoples business. You don't even know what she did with the kiddo previously. It doesn't mean she is a bad person. People are allowed to have breaks. Maybe she had an emergency. Stop assuming that you need to go report everything. How would you like it if your boss had a camera on you all day. Why don't you look at how you would feel reported on something silly or go up to the Nanny and tell them who you are at least and explain that it bothered you.