American children are getting fatter at an alarming rate, with the percentage of significantly overweight black and Hispanic youngsters more than doubling over 12 years and climbing 50% among whites, a study shows.

By 1998, nearly 22% of black children ages 4 to 12 were overweight, as were 22% of Hispanic youngsters and 12% of whites, according to researchers who analyzed data from a national survey. In 1986, the same survey showed that about 8% of black children, 10% of Hispanic youngsters and 8% of whites were significantly overweight. "Prior studies show it took 30 years for the overweight prevalence to double in American children," said Dr. Richard Strauss, a pediatrician at the University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School. This study should be "a call to action," said Strauss, who conducted the research with Harold Pollack of the University of Michigan. Among the reasons given for the increase: Children are spending much more time watching television, using computers and playing video games, and busy parents are relying more on fast food to feed their families.