Declan Hainey's body was discovered in his litter-filled cot about eight months after he was last seen alive.
His mother Kimberley, 38, was convicted of neglecting and murdering him but was released last April on appeal.
And yesterday, at an inquiry into his death, his mother's drug worker said she saw no reason for him to have been put on the Child Protection Register.
Declan, who was born in April 2008, was never placed on the confidential list, which details children the authorities believe are at a significant risk of harm, and he was found dead in his Paisley home in March 2010.
Hazel Martin told the inquiry: "Because of the information available and the stability of Kimberley Hainey, I don't think Declan should have been placed on the Child Protection Register."
Martin said her opinion was based on several meetings she had with Hainey and information she had been given by social workers.
When asked by Sheriff Ruth Anderson, who is presiding over the Fatal Accident Inquiry, if she thought the Haineys' case would require Child Protection measures at some point, Martin said: "I can't recall what my thoughts were at that time." But she added: "I didn't think at any time that Declan was a child who should be on the Child Protection Register.
"Kimberley was progressing well, she had stabilised very quickly."
She also told the inquiry at Paisley Sheriff Court that she had "no concerns over Kimberley's mental health".
The inquiry continues.