The four baby goats and 5-month-old baby kangaroo stolen from its mother's pouch at a Wisconsin zoo venue are still missing and zookeepers fear they may not survive.

The baby animals were reported missing from their insulated winter shelter on Wednesday a few miles away from the family-owned Special Memories Zoo in Greenville, Wis., but authorities still have no leads as of Sunday.

"[I was in] shock, disbelief...where did they go? What happened? Somebody had to remove them," zookeeper Gretchen Crowe, who first discovered the babies were missing, said.

Crowe made the discovery after seeing the pouch of the baby kangaroo's mother hanging out. The babies were fed by zoo employees Tuesday night.

"Unfortunately the babies have not been found yet but we know that the Outagamie County Sheriffs Department is doing everything they can to find them and whomever took them," Special Memories Zoo said on Facebook Saturday night.

"There's just bad people in the world," zoo owner Dona Wheeler told NBC News. "It's very, very upsetting."

The zoo plans to add surveillance cameras and more locks after the incident.

"I believe the baby kangaroo is dead," Wheeler told ABC News. "It cannot live without its mother, it cannot live without special formula, it cannot live without heat.. [If] a person took it who knew what they were doing it probably has a chance of living. But if somebody didn't... if someone did it as a joke, I'm sure by now it's probably dead."

"I feel absolutely horrible. We do everything in our power to keep animals alive," she added. "Right now my stomach is just turning to think somebody would do that."

The baby goats were intended to be part of the zoo's petting area.