The finding is reported in the Jan. 1 issue of the journal Pediatrics. It's based on a study of more than 2,600 kids raised near New Orleans and followed since the early 1970s.
The data cover almost 18 years and gave the researchers a long-term look at weight and fat patterns.
As kids, the participants' BMI was calculated, and their arm fat was measured with skin fold calipers. BMI is an indirect measure of body fat.
Distinguishing between BMI and skin fold fat let the researchers take participants' natural builds into account. The process was repeated many years later, when the kids had become young adults.
Extra fat and excess weight often lingered well beyond childhood.
Even the youngest kids were affected. The most overweight 2- to 5-year-olds -- those whose BMI was greater than 95% of children their own age -- were more than four times as likely to be too fat as adults.
"A child with high BMI for age is much more likely to become an obese adult than is a relatively thin child," say the researchers, who included the CDC's David Freedman, PhD. "Overweight children have a greatly increased risk for becoming overfat adults."