B.,
I too would be concerned that this little girl is running the neighborhood unsupervised. If you feel that this girl is too old to be playing with your children than that is what is correct. You make the rules. If you are uncertain on how to approach the Mother/Father of this little girl perhaps, for the time being, do what you CAN do to remedy your troublesome situation.
Why not tape a colored poster paper or something on the front door and explain to this little girl that whenever she sees this colorful paper on the door that she cannot ring your doorbell. Explain to her that your babies NEED their sleep and every time the colored paper is taped to your door that nobody is to ring your doorbell. At least this may eleviate your initial concern. The concern about confronting the girls Parents or concern over the little girl in general, can be handled when and if you are ready.
Isin't it a shame? We have a boy like this in our neighborhood or should I say........We have parents like this in our neighborhood.
I wish you well.
K.