"Children of parents who set consistent rules have a slightly lower body-mass index [BMI]; they're thinner," said study author Pauline Jansen.
Both mothers and fathers who enforced clear guidelines had a similar effect on their children's weight -- regardless of their own weight -- found Jansen, an honorary off-campus fellow at the Murdoch Children's Research Institute in Melbourne.
The study involved more than 4,000 children and their parents who participated in a long-term study of Australian children.
Starting in 2004 when the children were 4 or 5 years old, parents reported their offspring's height and weight and described their parenting styles four different times every two years.
Jansen found an association between consistent parenting and healthy weights in children, not a cause-and-effect.
And while the effects were not great, they were only slightly less than the effects of other factors often cited as contributing to a child's healthy weight, such as breast-feeding, said Jansen, now a researcher at Erasmus Medical Center in the Netherlands.
This suggests programs aimed at helping get children to a healthy weight should include talk about parenting styles, she said.
Childhood obesity is a troubling public health problem. In the United States, 17 percent of children aged 2 to 19 are obese, according to the U.S. Centers for Disease Control and Prevention, raising the risk of high blood pressure, high cholesterol, joint problems, diabetes and other conditions.
The new study is published online Nov. 25 and in the December print issue of the journal Pediatrics
What exactly is parental consistency? For the study, Jansen said, ''the parenting consistency we assessed did not refer to lifestyle habits, but was more global. It reflects the degree to which parents set and ensure compliance with age-appropriate instructions, rules and expectations. We showed that this global consistency benefits child BMI."
BMI is a measurement of body fat that takes height and weight into account.
Why would parenting style affect children's weight? Jansen didn't look at that specifically. However, she speculated that those who are consistent in parenting ''may be more likely to set clear expectations around healthy behaviors -- for example rules regarding television viewing, screen time and physical activity, bedtime routines and the timing and type of foods consumed."
One expert said the finding is a good starting point.
The study ''is a good first start to see the influence that both parents have" in affecting a child's weight, said Dr. Gloria Riefkohl, a pediatrician at Miami Children's Hospital. In future research, she said, "we need to take a look at the influence of expanded families," she said, such as the effect of grandparents. Researchers should also look at nontraditional families.
Parents can help encourage healthy weights in their children in a number of ways, she said. "Choose family goals, such as exercising every day and eating fruits and vegetables," she said. "Keep track of who meets their goals, and praise those who do. And when the whole family achieves the goals, do something fun together -- going to the zoo, park or aquarium, and so on."
Parents should also focus on establishing healthy eating habits early, Riefkohl said: "What we eat is a learned process."
To learn more about childhood weight, visit the U.S. Centers for Disease Control and Prevention.