The young Norwalk brother and sister found dead alongside their father early Monday morning had gone missing less than 12 hours earlier, when they were supposed to have returned home from a weekend visitation with their dad.

Officers unsuccessfully tried to locate them Sunday night but had no reason to believe they were in harm’s way, until a grim discovery in the garage behind an abandoned home the next morning, police explained Tuesday night.

Five-year-old Geselle Moncada and her 4-year-old brother, Jesus, had spent the weekend with their father, Yimi Moncada, per the parents’ custody agreement, Lt. Jared Zwickler said.

They were supposed to return home to their mother at 8 p.m. Sunday and Yimi Moncada had texted saying he would bring them there, but they never arrived, so their mother reported the pair missing late Sunday night, Zwickler said.

Police contacted Yimi Moncada’s mother, who said she last saw the children around 7:40 p.m. Sunday when he had supposedly brought them to their mother’s house, but he still could not be found, Zwickler said. Calls to his phone went directly to voicemail.

“At that time there was no additional information to believe the children were in harm, nor were any other locations given for officers to check,” Zwickler said Tuesday night. “Officers placed Geselle, Jesus, Yimi and the vehicle in a national database in an attempt to locate them.”

The next morning, however, patrol officers were called to a garage behind 8 Elizabeth Street in South Norwalk where they found the dead bodies of all three. Investigators determined the children were victims of a double-murder suicide and autopsies were completed on all three.

The children’s deaths prompted outreach from Norwalk Public Schools, which will provide phone and online access to grief counselors to students coping with the trauma of a lost classmate, despite studying remotely during the coronavirus pandemic.

“It is with deep sorrow that we learned today about the deaths of Rowayton Elementary Kindergarten student Giselle Moncada-Valdavinos and her little brother Jesus, along with their father, in a senseless act,” they wrote. “Our hearts go out to their family and friends, and we ask the entire community to hold them in your prayers.”

The commissioner of the Department of Children and Families confirmed late Monday that the agency was in contact with the family in 2015 after a domestic violence incident between Moncada and the children’s mother, but not the children themselves. The children’s mother filed for divorce the next year and the divorce was finalized in early 2017, court records show.

“This is a horrible incident that makes us feel great anguish for the loss of these innocent children, for their grieving mother, and the community members who knew them,” DCF Commissioner Vannessa Dorantes said in a statement.

“The Department last had contact with the family roughly 5 years ago,” Dorantes continued. “The mother had obtained a restraining order against the father due to domestic violence and concerns were expressed for an infant in the home. Upon assessment, the children were viewed as safe and their needs were appropriately being met. Our involvement ended as it was reported to the Agency that father completed court-ordered programming, the prior charges were dismissed and the restraining order had expired.”

Anyone with information that may help investigators is asked to call the Norwalk Police Tip Line at 203-854-3111 or send information through the Norwalk Police website at www.norwalkpd.com.

Anonymous tips can be texted by typing “NPD” into the text field, followed by the message, and sending it to CRIMES (274637).