Parents who argue are more likely to have babies with troubled sleeping patterns, research suggests.
Infants affected by rows at nine months old can have disrupted sleep when they are 18 months old, a study found.
Researchers from the UK and US analysed relationship quality and sleeping patterns in a group of more than 300 babies both when they were aged nine and 18 months. They discovered that how parents relate to each other influences children's sleep patterns.
Professor Gordon Harold, from the University of Leicester's school of psychology, who worked on the study, said: "Regulated sleep is essential during infancy for healthy brain and physical development. Disrupted sleep patterns early in life have serious implications
for children's long-term development.
"How couples/parents relate to each other, specifically how they manage conflicts in their everyday lives, is also recognised as having significant implications for children's long-term emotional, behavioural and academic development."
Because all the children in the study were adopted at birth, researchers were able to pinpoint the exact influence of a child's environment, rather than just looking at possible genetic similarities between parents and children.
Prof Harold said: "When parents and children are biologically related, any association between how parents behave and attributes of child behaviour may be explained by common genetic factors - the same genes underlying parent and child behaviour.
"The present study rules this explanation out in that parents/caregivers and children are not genetically related, so common genetic factors cannot account for the associations noted.
"This study does not negate the importance of genetic (nature) and biological factors underlying children's development but does locate the dynamic between couples as a unique family "environmental" influence (nurture) on children's early development."
The study was published in the journal Child Development.
PA