Having an older mom. Older moms are more likely to have obese kids, according to numerous studies. A 2007 study in the journal Archives of Disease in Childhood found children born to women ages 30 or older had 2.6 to 2.8 percent more body fat than children born to women younger than 25. And a 1997 study in the Journal of the American Medical Association found obesity was higher among 9- and 10-year-old girls whose moms gave birth after age 35, compared with girls whose moms gave birth when they were 21 or younger.