Benjamin Nicholas Houghton, 40, and Yue Ning Lieu, 42, are in custody after police discovered the child during a welfare check at a Glen Osmond motel in Adelaide's south on Saturday.
"The infant had been deceased for a period of time," South Australia Police said in a statement on Tuesday.
A post-mortem confirmed the boy was aged between six and seven months old, police said.
The man and woman had been living at the Tollgate Motel since they arrived in SA at the start of the year, police said.
"They have not had contact with South Australian authorities since this time," a police statement said.
Houghton and Lieu have been charged with criminal neglect and destroy human remains to pervert the course of justice.
Their matters appeared in Adelaide Magistrates Court on Monday.
They did not apply for bail and were remanded in custody until May 3, 2027.
SA Police's Eastern District detectives conducted the initial investigation.
"However, due to the nature and complexity of the incident and the resources required, Major Crime Investigation Branch have taken over the investigation," a police statement said.
"Police are seeking assistance from anyone who has stayed at the Tollgate Motel, and specifically anyone who has information about the occupants of room four to contact Crime Stoppers."
14°C