Lynsey Jones told the hearing she looked through the letter box of the property where tragic Declan Hainey lived with his mother Kimberley Hainey on March 17, 2010, but did not see anything of note.
Ms Jones told Paisley Sheriff Court yesterday the visit with a male colleague took place because the 23-month-old child had not been seen for months.
They first went to the cottage flat in the town on March 16 to try and see the child but there was no answer. Senior social worker Julie Dynes, told them to try again the following day, the court heard.
The following day, Ms Jones and the man attended again and knocked on the door, without answer, before she looked through the letter box.
Asked by fiscal depute Stuart Cassidy what was inside the, Ms Jones replied: "Nothing."
As Ms Jones left she met Ms Hainey's downstairs neighbour who said he had not seen the heroin addict mother, or her son, for months.
He also told the social worker he had not heard Declan running about the house, or heard any noise from the property in so long he thought the flat had been abandoned and nobody lived there anymore.
But Declan was still in the flat, lying dead, mummified in his litter-filled cot in his nursery. Ms Hainey was jailed for life for the boy's murder, but later released after the conviction was overturned on appeal. The fatal accident inquiry continues.