Nearly 200,000 babies in Britain are at high risk of suffering abuse because they are born into families with problems of domestic violence, mental health or addiction, new research suggests.
The NSPCC said under-ones were eight times more likely to be killed than any other age group in childhood.
Launching a new campaign to support the most vulnerable babies, the charity released the first estimates of how many infants are living in high-risk family situations.
Across the UK, 144,000 children under one live with a parent who has mental health problems, 109,000 have a parent with drug or alcohol problems, and 39,000 are in a home affected by domestic violence. Some fall into more than one category.
Two-thirds of official inquiries into cases where babies are killed or seriously injured involve one or more of these factors.
There has been heightened concern about how agencies care for vulnerable young children since the death of 17-month-old Baby P - now named as Peter Connelly - while on the at-risk register in August 2007.
The NSPCC's campaign, named All Babies Count, calls for "early and effective" support for babies living in homes with these problems.
The charity said babies who suffered trauma, abuse or neglect were more likely to develop behavioural problems in childhood, anti-social behaviour in adolescence, and physical and mental health problems - including heart disease - in adulthood.
NSPCC chief executive Andrew Flanagan said: "All Babies Count is about making sure all babies get the care they need, when they need it most. Evidence from early intervention programmes shows that intervening early can remove the future risk of abuse or neglect.
"And it also makes sound economic sense. Investing in preventing harm is a more effective way of spending money than trying to pick up the pieces of children's broken lives in the years after abuse has happened."