Researchers looked at 2,556 pairs of twins in England and Wales when they were aged 4 and 10. The investigators focused on 28 genetic variants known to be associated with obesity risk.
The study also looked at each child's body-mass index (BMI), which is an estimate of body fat based on height and weight, at both ages.
The results indicated that the influence of the genetic variants rose over the years. In other words, genes appear to be responsible for 43 percent of the difference in size among kids at age 4, but 82 percent of the difference in size among kids at age 10, the study authors pointed out.
The findings, published in the current issue of the journal Obesity, confirm results from previous studies, according to the researchers.
"Our results demonstrate that genetic predisposition to obesity is increasingly expressed throughout childhood," study co-leader Dr. Clare Llewellyn, of the department of epidemiology and public health at University College London, said in a university news release.
"This underlines the importance of intervening at an early age to try to counteract these genetic effects and reduce childhood obesity," she added.
The U.S. Department of Agriculture has more about keeping children at a healthy weight.