Parents who express negative emotions toward their infants, or handle them roughly, may be inadvertently harming their babies' psyches, new research suggests. This type of "negative parenting" results in aggressive, defiant kindergarteners and even affects adult behavior, the researchers said.
"Before the study, we thought it was likely the combination of difficult infant temperament and negative parenting that put parent-child pairs most at risk for conflict in the toddler period," study researcher Michael Lorber, of New York University, said in a statement. "However, our findings suggest that it was negative parenting in early infancy that mattered most."
Aggressive behavior is fairly common in toddlers, but in most cases, this drops off by the time they reach age 5. In children whose aggressive behavior does not stop, they have a pretty good chance of staying that way, Lorber said.
"Conduct problems around age 5 are probably one of the strongest predictors of anything that you care to predict for years to come, including depression, substance use, academic problems and peer rejection," Lorber told LiveScience. "They predict even aggression against one's romantic partner later in life." [11 Facts Every Parent Should Know About Their Baby's Brain]
The researchers studied 260 mothers and their children from birth until first grade. The sample was selected from mothers who received prenatal care from a public health clinic, a "high-risk urban sample," selected between 1975 and 1977.
The researchers assessed the infants' temperaments and the mothers' parenting styles in the first six months of life (by observing the pair during feeding time) and during the toddler years through observational and parental reports. The researchers followed up with the mothers and the children's teachers when their kids were in kindergarten (ages 5 and 6), asking them to rate the children's behavior.
The researchers found that children who exhibit aggressive, defiant and explosive behavior by the time they're in kindergarten very often have tumultuous relationships with their parents from early on.
"Moms that did more of that stuff, that was a stronger predictor of conduct problems later on," Lorber said. "In toddlerhood in the pairs where the mom had been negative to the kid during infancy, the mothers were more hostile and the kids were more angry in a series of teaching tests."
What they didn't find was a correlation between difficult early-life behaviors of the child (if the child was irritable or quick to switch mood in his or her first six months) and later aggressive actions and attitudes.
The negative activity of parents in an infant's first few months of life seems to start this cycle, the researchers say; negative parenting results in highly angry toddlers, the research finds, thus spurring more hostility from mothers.
It is possible that such negativity could be caused by an outside source, possibly the family's genetics or even the environment around them during those early years. Either way, the findings from infancy also carry on to later in life for the study participants.
"This study's been going on now for over 30 years," Lorber said. "We've found that those parenting measures, those feedings in infancy, not only predict early conduct problems, but 26 years later, those children we saw as babies, they are more aggressive as adults."
Discovering what causes these overly aggressive toddlers could help researchers design and implement appropriate interventions to prevent negative parenting before this cycle develops.
"If you want to prevent conduct problems before they start, you would want to do something in infancy," Lorber said. "Even in the first six months you would want to do something to improve the parent-child relationship."
The study was published today (Oct. 26) in the journal Child Development.
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Jennifer Welsh is a Connecticut-based science writer and editor and a regular contributor to Live Science. She also has several years of bench work in cancer research and anti-viral drug discovery under her belt. She has previously written for Science News, VerywellHealth, The Scientist, Discover Magazine, WIRED Science, and Business Insider.