I understand you think that if you try to report this girl must be having issues the landlords will know it was you.

I was thinking that maybe one way to deal with it is you said the girl goes to school right? Well, maybe you could find a way to annonymously get in touch with the guidance councelor at the school and quietly ask her/him to observe the girl closer.
And you COULD call child services annonymously, I did that myself.

However if you contacted the school and they watch her more carefully, if something is presented to these parents it would be coming from the school and not you.

From what you discribe, it doesn't sound like these parents truely engage and parent this child at all. Do you ever hear the mother reading to her or taking time out to spend with this child? Well, children get lonely, thrive attention and if they don't get it they CAN do strange things to gain attention. It sounds to me like the girl is trying to seek attention by talking with friends that are not there and ofcourse you, someone who is responding to her somehow.

Open Eyes