"I got comments all the time from my so-called friends," says Lan Ma, recalling that her two children, as infants, had chipmunk cheeks and "rolls after rolls of flesh."

Ma, of Edgewater, N.J., ignored any suggestion that Thomas, now 4, and Tyler, 2, were too big, even when both weighed in at 14 pounds, double their birth weights at their 2-month checkups. "I was never worried about their weight when they were young, because they were both very, very healthy."

Some other parents, however, can become anxious, given widespread reports that an increasing percentage of children and adolescents in the United States are overweight.

"With all the talk about obesity, we certainly have some overzealous parents who are worried about their nice, healthy, chunky baby becoming an overweight adult, and (they are) restricting their nutrients," says Dr. Robert Holmberg, a pediatrician in Bangor, Maine, and a member of the American Academy of Pediatrics Task Force on Obesity.

When should "baby fat," long the symbol of a thriving infant, be cause for alarm?

In general, a chubby baby is a healthy one, doctors say.

Poor nutrition and lack of exercise - major factors in the obesity epidemic among children and adults "haven't had time to affect the infant," Holmberg says.

But while doctors urge parents not to panic, they also encourage them to watch for warning signs:

- Before age 3, parental obesity is a stronger predictor of future weight problems than an infant's birth weight or place on the growth chart.

"If parents are overweight, their children are at much greater risk for the development of weight problems," says Dr. William Dietz, director of the division of nutrition and physical activity for the Centers for Disease Control and Prevention.

Genetics may be partly to blame, but more often the culprit is lifestyle, says Dr. Thomas Robinson, associate professor at the Stanford University School of Medicine and director of the Center for Healthy Weight at Lucile Packard Children's Hospital.

"A child is raised and learns about feeding, eating and activity in that same environment" as the overweight parent, he notes in an e-mail interview.

- A sustained growth spurt before age 4, in which weight increases more rapidly than height, is another possible warning sign, Holmberg says.

And parents should note if weight appears to be interfering with developmental milestones, such as walking.

Still, always consult a pediatrician before changing your baby's diet.

Several studies suggest that breastfeeding, in addition to its nutritional advantages, lowers the risk of obesity later in childhood. Adds Dietz, "the longer the children are breastfed, the lower the risk." The AAP recommends breast milk for at least the first year.

Parents should also use this time during infancy to establish healthy routines for the entire family, doctors say. For instance:

- Keep junk food out of the house.

"It is amazing to me how many young children, even under a year of age, are fed sugar-sweetened soft drinks and French fries and other fast foods," Robinson says. "If a parent eats junk food and has it in the home, that is the food their child will learn to eat, no surprise."

Other than the occasional chicken nuggets, or birthday cake at school, Ma steers her kids away from processed foods and avoids them herself, opting instead for fresh vegetables, chicken and fish. She sends her son to preschool with bananas and rice crisps for snacks.

"A parent is always so much more effective as a role model than as an instruction book," says Ma, a project manager for IBM and author of the e-book "You Can Have It All: Baby, Career and Plenty of Sleep."

- Limit TV time for everyone.

The AAP recommends no viewing for children under 2, but Robinson notes that it's hard to discourage kids of any age from watching too much TV if mom and dad aren't setting a good example.

"This is a good time for them to consider reducing the number of TVs in their home and watching less themselves," he says.

- While regular exercise is important for toddlers, infants get their workouts naturally by learning to lift their heads, roll over, sit up and crawl, says Celia Kibler, owner of Funfit, Inc., a Maryland-based fitness center for kids. "A baby at 6 months should have no trouble achieving the muscle tone it needs," says Kibler, whose classes for infants focus on bonding with parents, not working out.

- In what may be the toughest advice to follow, Holmberg encourages parents to resist the urge to compare their babies with others.

"That's a very dangerous thing to do," he says. "All babies are different."