There have been reported sightings of the little girl for a very long time on Earth with little evidence to back up claims. Most of these sightings take place on space vessels of some kind though some have been reported from on stations or outposts.
The little girl phenomena is one where a crew person or group of crew people initially hear the sobbing of a small child. In almost all cases this sobbing comes from a part of the station or ship where no child should (sometimes even could be, as in, no children are aboard the ship). Upon investigating they finds the electrical disturbances in the power system cause the standard environmental conditions to be disrupted. At least two thirds of people have reported doing a full search, still hearing the sobbing child, but unable to find its source of the sound. While the remaining one third of cases state finding a small child, sobbing.
Appearance
Exactly what the child looks like is a point of contention. Even when the witnesses in question have been skilled artists they report that try as they might they cannot get the image to look right. There is some agreement, she appears to be between the ages of 4 and 6, wearing a white night gown that goes to just below her knees, it is frilly but simple. She is barefoot and has her hair braided into a pony tail. Her eyes are always blue, though her hair color varies from dirty blond to nearly black. She is always seen holding a thread-bear stuffed bear by the arm.
Different races have perceived her differently. While attempts to sketch or draw the child always results in a human (or very similar) child, each witness also reports that they have perceived her as of the same race as them and do not remember questioning why say, a human girl is sighted crying on a Romulan starship. If asked, the witnesses always report that they could have sworn the girl was of the same race. Descriptions and details also always perplex the witness when they expect to be able to describe pointed ears, forehead ridges, or some other marking of race and cannot.
Detection
Sensors, cameras, and other sensing devices are unable to located or capture an image of either the little girl or the sounds. However, using the help of Vulcan Mind Meld as well as of some Betazoid investigators it has been established that to the witness, the sounds and visuals are real. To date, no technological device has been able to record an image of the little girl or the sound of her crying.
Non-Human Witnesses
On at least 27 different occasions a non-human was present during the event. Of those 14 of them were in the presence of someone with innate psychic abilities.
Vulcan Sightings
Of those 14 occasions 10 of which were in the presence of Vulcans in each of those cases the Vulcans report that the crying sound itself seems to carry with it an additional psychic presence. They find the crying increasingly uncomfortable and while most refused to describe the encounter further, those that did described it as tugging at their emotional control making it more difficult to maintain during the encounter.
Upon seeing the little girl, the only Vulcan who has been known to do so reported that the girl felt cold to her mind, like a void.
Betazoid Sightings
Two of the remaining occasions occurred in the presence of fully telepathic Betazoids. Each of these cases report that it felt like the crying was not only outside but inside their head and while they found the experience uncomfortable they also note that the crying felt inside their mind resonated as genuine fear and sorrow. When attempting telepathic communication or trying to use telepathy to better zero in on the source of the effect, each report they felt a wall. Neither of those witnesses saw the child.
Romulan Sightings
Romulan sightings have been rare, there are only 4 known cases though it is possible there are more. In 3 of those the Romulan witnesses were unable to find the source of the sound and the Romulan commander ordered the part of the ship sealed - then ordered the ship back to space dock for communication problems. Each each of the three cases, the ship was ordered to be searched after it was evacuated. In the 4th case, the little girl was found and the Romulan commander ordered that she be brought to sick bay.
Physical Contact
Physical contact with the little girl is dangerous. When touched she responds violently, screaming. The scream seems to have the ability to echo throughout the entire ship and universally fills those who hear it with an intense feeling of absolute terror. On numerous occasions people of various races have decided to attempt and take the girl to a superior, to sickbay, or some other location. When approached with the intent to touch, she shakes her head vigorously and the crying gets worse.
Inevitably once the child screams, she vanishes leaving behind an intense feeling of terror and fear that lingers in the area she was sighted for days, one report said the effect lasted for weeks.
Harm
Four Klingon sightings reported the commanding officer ordered security to fire upon the girl, noting that no real child could have produced the evidence in question. Cardassian reports hold similar, that on a few occasions security forces were ordered to eliminate the threat. In each case, the effect is the same as attempting to touch the girl, when the witnesses turn violent, she screams and vanishes.