The Wander Hills Children are victims of their former headmistress, Ellen Gold in life and death. Due to the trauma of their lives and untimely deaths, their ghosts were tethered to Gold as well.
After the death of two children in 1898, a police investigation found Ellen Gold was responsible for them dying of malnutrition. Gold was bailed out by her brother and resumed her duties at the Wander Hills Orphanage. While a lightning storm raged outside, Gold locked all the children in their rooms but neglected to free them when a fire spread to the building. As a result, the children inside burned to death.
In 1944, the children of three families living in an apartment, built at the time over the grounds, reported seeing the ghosts of children before they tragically passed away two days later. In the 1990s, the Ghostbusters confronted the ghost of Ellen Gold. Gold retaliated by throwing children at Ray Stantz and Egon Spengler. Once Gold was trapped, Wander Hills and the children dissipated for good.
During the Tiamat incident, Ray and Egon were forced to manually vent the Containment Unit or risk a very big explosion taking out Tribeca. Ellen Gold was released from the unit and attempted to manifest Wander Hills. The Ghostbusters, minus Winston, engaged Gold who attacked them with Wander Hills Children again. One of the children was thrown right in Egon's face.
The children are possibly tethered by Ellen Gold's manipulation of P.K.E. generated by their constant state of fear.