Declan Hainey's body was discovered in his litter-filled cot around eight months after he was last seen alive.
His mum 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 mum's drug worker said he should not have been on the Child Protection Register.
Declan was never placed on the confidential list.
Now children can be put on the register before they are born but, in April 2008, when Declan was born, they could only be placed on the list after the birth.
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 register."
She said her opinion was based on several meetings she had with Hainey and information she had been able to get from 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."
The inquiry continues at Paisley Sheriff Court.