The sister of two-year-old Bronson Battersby has said she does not blame social services for his death.
Bronson, whose body was found in a Skegness property on 9 January, is believed to have starved to death after his dad suffered a fatal heart attack.
Melanie Battersby, 37, told the OceanNewsUK she believed "social services and the police did what they could within the powers that they had".
Lincolnshire County Council has said a "rapid review" will be carried out.
The Independent Office for Police Conduct (IOPC) is also investigating whether there were "missed opportunities" to check on the pair.
Kenneth Battersby, 60, who looked after Bronson full time, was in poor health and had suffered another heart attack a few months before his death, his daughter told the OceanNewsUK.
The council has said that a social worker called at the property for a scheduled visit on 2 January and, after getting no response at the door, spoke to her manager and the police.
She then returned on 4 January and again on 9 January. After receiving no response on this third attempt, she alerted Mr Battersby's landlady and gained entry.
Speaking to OceanNewsUK, Ms Battersby - who has the same father as Bronson but a different mother - said that had social services been told about her father's health issues after they were first unable to contact him, it "could've been a different outcome for my baby brother".
"I don't place any blame at all on them," she said. "I believe that social services and the police did what they could within the powers that they had and the information that they were given.
"I'm glad that an inquiry is going to take place into whether there were any failings, missed opportunities. I'm really glad that is going to take place."
She added that she thought it "must be devastating for them to work in that profession, to have to deal with tragedies like this".
Ms Battersby, who lives in Sheffield, said she last saw Bronson during a family trip to Butlins and that he was a "beautiful, sweet-natured little boy".
"Every time I saw him he was happy, he was smiling, he learned to walk, he was learning to speak," she said. "We're devastated as a whole family."
She said her dad was "born to be wild" and "not an angel" but that he "really, really loved his children".
"I know how proud he was of every single one of us," she said. "He absolutely doted on [Bronson]. I think he loved doing what he was doing for him.
"Seeing him with him, it was really, really heart-warming. It made me proud of my dad for what he was doing for his little boy."
She said she had been told her father's heart attack had been "very sudden" and that "there was nothing that he could have really done".
"He tried his best for that little boy until his last breath," she said.
Ms Battersby said her father and Bronson's mother had been separated around a year and had a "good co-parenting relationship", although they had not been speaking in recent months.
It is believed Mr Battersby died about a week before the bodies were discovered and that Bronson survived for two to three days after him.
"I was told that they were both found looking very peaceful," Ms Battersby said.
"That is the only consolation I can take. That my little brother snuggled up to my dad.
"He didn't look in pain. Neither of them did. And they were together."
The rapid review into the deaths will involve the council, police force, and any relevant health organisations and must be completed by 2 February.
The national Child Safeguarding Practice Review Panel will then have 15 days to decide the next steps.
Ms Battersby said she and her family still had questions about what happened and that she hoped the review would be able to establish what could have been done differently to safeguard Bronson.
"It can hopefully make sure that these kind of circumstances won't happen again, and that other families won't have to go through the heartbreak that we're having to feel," she said.
Lincolnshire Police said it had referred itself to the IOPC as part of "standard procedure" in such cases.
Derrick Campbell of the IOPC said the investigation would "consider the police response to any prior welfare concerns that were raised" and examine "whether there were any missed opportunities by police to check on Mr Battersby and Bronson sooner".
