Simon Smith was jailed in 1996 after murdering three-month-old Lauren, six-month-old Jamie and Eleisha, 10 months, between 1989 and 1994 in Staffordshire.
The Parole Board has recommended that Smith is now suitable for a move to an open conditions prison.
Lauren's mother Rachel Playfair said she would do anything she could to get the decision overturned, describing Smith as "pure evil".
Eleisha and Jamie, Smith's children from a previous marriage, were first considered to be cot death cases but an investigation started when Mrs Playfair's daughter Lauren died of asphyxiation a year after Jamie's death.
Smith had been kept in a secure prison by the Parole Board two years ago.
Mrs Playfair told the BBC: "My victim impact (statement) played a big part in keeping him in a secure jail.
"How, in two years, can he suddenly not be a risk to the public?
"My biggest fear is that he will be released from prison and find another woman. He's only 50, so he can father another child."
Mrs Playfair added: "He is pure evil. He only killed his own flesh and blood.
"The judge repeatedly said life means life. What he did was premeditated. He knew exactly what he was doing."
A spokesman for the Parole Board said in a statement: "The Parole Board has made the decision not to release Simon Smith following an oral hearing in January 2019 but has recommended that he is suitable for a move to an open conditions prison.
"We will only make a recommendation for open conditions if a Parole Board panel is satisfied that the risk to the public has reduced sufficiently to be manageable in an open prison.
"This is a recommendation only and the Ministry of Justice will now consider the advice and make the final decision."