Children aged up to three are "more malleable", the report says
Unborn babies whose mothers suffer stress or illness or use drugs or alcohol can be more susceptible to both good and bad parenting, a study claims.
Depending on the care they get, says the study, these children can do better or worse than their peers in developing skills such as application and empathy.
Think tank Demos said targeted support for families of at-risk children could help them "buck the trend".
Demos analysed data from more than 9,000 UK households for its report.
The Building Character report says there are two main theories why some children are more susceptible to the influence of good and bad parenting.
It could be a result of evolutionary natural selection, or another possibility is that "different pre-birth factors, including the ill-health or stress of the mother, may be hardwiring heightened susceptibility into the developing baby even before the child is born".
Demos calls for targeted intervention to help parents provide a warm and consistent upbringing that encourages children to develop crucial skills such as application, self-regulation and empathy.
Report co-author Richard Reeves said: "No government can ignore the fact that some parents need more support than others: we must end this conspiracy of silence."
The report says its analysis suggests "the situation of at-risk children may be both graver and more hopeful than previously assumed".
"In the case that differentially susceptible children are subjected to poor quality childcare, poor parenting, or the detrimental effects of poverty itself, their risk is increased substantially - it is risk squared.
"On the other hand, if interventions occur in the right way and at the right time, children with a poor start in life have every opportunity to make up for lost ground and even exceed their more advantaged peers: differential susceptibility may be one of the factors in what helps certain kids to 'buck the trend'."
Mr Reeves called parenting "the final frontier for issues of social justice and social mobility".
"If we want to seriously address social mobility in the UK it must start in the home and with children under the age of five," he said.
The Building Character report has also suggested that an upbringing of "tough love" makes children more successful in later life.
A balance of warmth and discipline from parents improved children's social skills more than a laissez-faire, authoritarian or disengaged upbringing, it suggested.